1973–1987 Chevy & GMC Square Body Cab Replacement Guide: C10, K10, C20, K20, C30 & K30 Builds

The 1973–1987 Chevy and GMC Square Body has become one of the most popular classic truck platforms being restored and customized today.

Whether you call it a Square Body Chevy, Squarebody, C10, K10, C20, K20, C30, K30, Silverado, Sierra, Chevy pickup or GMC pickup, one problem continues to affect these trucks more than almost anything else:

Rust.

After four or five decades on the road, many original Square Body truck cabs need far more than a couple of patch panels.

Floors are rusted. Rockers are gone. Cab corners have disappeared. Cowls have deteriorated. Door openings have moved. Firewalls have been cut or modified, and decades of previous repairs can leave a restoration shop trying to rebuild a cab that is no longer square.

That leads to one of the biggest questions Square Body owners are searching today:

Should I repair my original Square Body cab or replace it with a new reproduction cab?

At Rust Belt Offroad, we build complete 1973–1987 Chevy and GMC Square Body replacement cabs for customers building everything from stock restorations to LS-swapped street trucks and 4x4 K-Series builds.

Here is what you should know before starting yours.

What Trucks Are Considered 1973–1987 Square Bodies?

The third generation Chevrolet and GMC pickup debuted for the 1973 model year.

Although Chevrolet officially referred to the design as the Rounded-Line generation, enthusiasts eventually gave these trucks the name that stuck:

Square Body.

The platform includes many of GM’s most recognizable pickups, including:

• C10 – ½-ton 2WD
• K10 – ½-ton 4WD
• C20 – ¾-ton 2WD
• K20 – ¾-ton 4WD
• C30 – 1-ton 2WD
• K30 – 1-ton 4WD

Chevrolet and GMC both used the basic cab architecture, although trim, grilles, badging and other exterior details differed.

For builders searching for a 1973 Chevy C10 cab, 1985 K10 cab, 1986 C20 cab, or virtually any other pickup within the 1973–1987 generation, the condition and geometry of the cab itself can determine how easy—or difficult—the remainder of the project becomes.

Why Are Good Original Square Body Cabs Getting Harder to Find?

Anybody who has restored one of these trucks in Ohio, Pennsylvania, Michigan, New York or elsewhere in the Rust Belt already knows the answer.

Salt and moisture were not kind to them.

Common rust areas include:

Rocker panels and inner rockers

Rust commonly begins from both the outside and inside of the rocker structure.

Cab corners

This is one of the first places many restorers inspect when shopping for an original Square Body.

Floor pans

Water intrusion, damaged weatherstripping and road salt can destroy the floor and surrounding structure.

Cab mounts and floor supports

Once rust moves into structural areas, the repair becomes more involved than simply welding in a cosmetic patch.

Cowl areas

Rust hidden beneath surrounding panels can become a major restoration project.

Windshield areas

Leaks around the windshield can allow corrosion to spread into areas that are difficult to properly repair.

Then there is another problem that isn’t always visible in photographs:

Previous repairs.

A 40- or 50-year-old truck may have been repaired several times already. Panels may have been welded over rust, openings may no longer be square, and old collision damage may not become obvious until the truck is completely disassembled.

That is why buying a cheap used cab does not always mean buying a cheap cab.

Repairing an Original Square Body Cab vs. Starting With a New Cab

There is absolutely nothing wrong with saving a good original cab.

If the structure is solid and the truck only needs limited rust repair, keeping the original sheet metal can make perfect sense.

The calculation changes when the repair list begins looking like this:

floor pans
rockers
cab corners
cab supports
kick panels
cowl panels
roof repair
firewall repair
door-opening repair

Each individual replacement panel may seem inexpensive.

Labor is not.

A restoration shop has to remove damaged steel, clean the surrounding metal, fit the new panels, weld them in, grind and finish the welds, repeatedly measure the cab and make sure every repaired section works with the next.

A restoration guide published this year made essentially the same point: body restoration is often a math problem, because inexpensive patch panels can turn into substantial labor once rust exists throughout multiple areas of the truck. 

At some point, builders need to compare the cost of repairing the old cab with the cost of beginning with a completely assembled replacement.

What Comes With a Rust Belt Offroad 1973–1987 Square Body Cab?

This is where our approach is different from buying a stack of loose reproduction panels.

Rust Belt Offroad currently offers a fully assembled 1973–1987 C/K Square Body cab built to order.

Our base cab includes major assemblies such as the floor and cross rail, doors, hinges, latches and strikers, dash structure, rear cab panels, cowl components, A-pillars, kick panels, windshield structure, roof structure and other components. Customers can select a 2WD or 4WD floor configuration and choose between an original-style firewall with A/C provisions or a smooth firewall. 

That means you aren’t buying a giant pile of sheet metal and then paying a restoration shop to figure out how all of it goes together.

You are starting with an assembled cab.

Want the Front Clip Installed Too? We Can Do That.

This is especially important for customers searching things like:

complete Square Body cab

C10 cab with front clip

73-87 Chevy cab and front end

Square Body replacement body

complete C10 body

Rust Belt Offroad also offers the cab with the front clip fully assembled and installed.

That configuration adds components including the left and right front fenders, inner fenders, radiator core support and a standard or cowl hood with hinges. 

Why does that matter?

Because front-end alignment can consume a tremendous amount of time during a restoration.

Fenders, hood, doors, cowl and radiator support all interact with one another. One panel being slightly out of position can affect several other gaps.

By installing and aligning these major components together during the body build, much of that work is already addressed before the body reaches the customer.

The Difference Is How the Cab Is Assembled

Buying reproduction sheet metal is only the beginning.

How those panels are assembled matters just as much as the panels themselves.

At Rust Belt Offroad, our bodies are assembled in-house using industrial water-cooled resistance spot welding equipment rather than simply plug welding the structure together.

Our fixtures are designed around original body datum points, and the assemblies are checked for alignment during construction.

That matters because the real goal isn’t simply to make something that looks like a Square Body cab.

The goal is to produce a cab where the:

doors fit correctly,
windshield opening is correct,
roof is properly positioned,
rockers align,
firewall is located correctly,
front sheet metal can be aligned,
and the completed cab sits properly on the chassis.

Our current Square Body program uses fixture-built assembly and factory-style resistance spot welding, with additional weld density intended to improve rigidity and panel fitment. 

2WD vs. 4WD Square Body Cabs

Another common search is:

Are C10 and K10 cabs the same?

They share much of the same cab structure, but builders still need to pay attention to floor and transmission-tunnel requirements.

A C10 or C20 2WD build may require a different floor configuration than a K10, K20 or K30 4WD build, particularly depending on the drivetrain and transfer-case setup being used.

That is why we offer both 2WD and 4WD floor configurations when building our Square Body cabs. 

When ordering a cab, we recommend knowing what chassis, transmission and drivetrain combination you intend to use before the build begins.

1973–1980 vs. 1981–1987 Square Body Front Ends

Another important distinction is the change GM made beginning in 1981.

Although the cab architecture remained recognizably Square Body, the front sheet metal changed substantially.

The 1973–1980 trucks use the earlier hood, fender and front-end styling, while the 1981–1987 trucks use the later front design.

That becomes particularly important when ordering a complete cab with the front sheet metal installed.

Rust Belt Offroad’s existing C/K identification guide covers many of the year-to-year differences, including the 1981 facelift. 

For customers who aren’t sure exactly which configuration they need, we would rather discuss the build before it begins than have someone order incompatible components later.

What About a Smooth Firewall?

This has become especially popular among restomod builders.

A traditional restoration may call for the factory-style firewall.

But if you’re building an:

LS-swapped Square Body

Coyote-swapped custom

big-block C10

pro-touring C10

show truck

or a highly detailed engine compartment, a smooth firewall can dramatically clean up the appearance of the engine bay.

Our Square Body cabs can be ordered with either an original-style firewall with A/C provisions or a smooth firewall, allowing the cab to better match the direction of the build. 

Square Bodies Are No Longer Just Cheap Old Work Trucks

This is one of the biggest changes we’ve watched within the classic-truck market.

For years, Square Bodies were inexpensive trucks people drove to work, plowed snow with, hauled trailers with and used around farms.

That is changing.

Today these trucks are being built as:

restored Silverado and Sierra pickups,
lowered C10 street trucks,
K10 and K20 4x4 builds,
LS-swapped restomods,
big-block muscle trucks,
diesel conversions,
pro-touring builds,
show trucks,
and high-end custom builds.

Enthusiast discussion around the introduction of complete replacement cabs has even centered on the fact that builders can now assemble what is effectively an entirely new Square Body using available reproduction components—something that would have been extremely difficult years ago. 

And as values rise, builders are looking differently at the economics of putting hundreds of hours into a severely rusted original body.

Starting With a Straight Cab Changes the Entire Build

Ask any experienced restoration shop what happens when the foundation of a vehicle is wrong.

Everything afterward becomes harder.

Door gaps become harder.

Glass fitment becomes harder.

Weatherstripping becomes harder.

Front-end alignment becomes harder.

Paint and bodywork become harder.

This is why we spend so much time on fixtures, measurements, welding and alignment before a cab ever leaves Rust Belt Offroad.

We aren’t trying to build the cheapest reproduction truck body.

We are trying to build a foundation that makes the rest of the customer’s project easier.

We Can Take the Build Further

Not every customer wants the same starting point.

Some customers want a bare assembled cab so their own shop can take over.

Others want us to take the project considerably further.

Rust Belt Offroad offers additional services including:

epoxy primer

bodywork and paint

bedliner

front sheet-metal installation

custom body modifications

and even mechanical work depending on the scope of the project.

Our Square Body program has grown beyond simply selling replacement sheet metal. The objective is to give customers options ranging from an assembled replacement cab to a much more complete starting point for their restoration. 

How Much Does a New 1973–1987 Square Body Cab Cost?

As of this writing, Rust Belt Offroad lists its fully assembled 1973–1987 C/K Square Body cab at $12,999.

The 1973–1987 Square Body cab with the assembled front clip is currently $15,499. 

Because our cabs are built to order, lead times vary.

Shipping is available by open or enclosed transport, and customers can also pick their cab up directly from our Canfield, Ohio facility. 

Is a New Square Body Cab Right for Your Build?

If your original cab only needs a cab corner and a small floor repair, replacing the entire thing probably doesn’t make sense.

But if you are staring at a cab that needs floors, rockers, corners, supports, cowl work, firewall repairs and previous collision damage, do the math before spending months repairing it.

The cheapest piece of sheet metal is not necessarily the least expensive way to finish a truck.

For many serious restorations and high-end builds, starting with a straight, rust-free, fully assembled cab can eliminate a tremendous amount of fabrication and uncertainty.

And that’s exactly why Rust Belt Offroad began building them.

Building a 1973–1987 Chevy or GMC Square Body?

Whether you’re building a 1973 C10, 1977 K10, 1980 C20, 1984 K20, 1986 C10, 1987 R10/V10, or another Chevy or GMC Square Body project, we can help you determine the right cab configuration for your build.

Rust Belt Offroad builds reproduction classic truck bodies right here in our Canfield, Ohio facility using fixture-built assembly, precision alignment and factory-style resistance spot welding.

Built Better. Built Here. Built to Last.

Contact Rust Belt Offroad to discuss your 1973–1987 Square Body project, current lead times, shipping options and custom build requirements.