Square Body Trucks: Why GM's 1973 to 1987 C/K Pickups Rule the Truck Scene

The square body went from work truck to blue chip in a generation. Hagerty now calls the 1973 to 1987 trucks among the most collectible American trucks, and the reasons are not complicated. GM built them for a long time, in nearly every configuration imaginable, on a simple ladder frame with an engine bay that welcomes modern V8 swaps.

What counts as a square body

GM called the 1973 redesign the Rounded Line generation internally; everyone else called it the square body. It was the third generation of the C/K line. C meant two-wheel drive and K meant four-wheel drive. Chevrolet used 10, 20 and 30 for half-ton, three-quarter-ton and one-ton trucks, while GMC used 1500, 2500 and 3500, badged 15, 25 and 35 from 1973 to 1980.

The pickups people mean by square body run from 1973 to 1987, but the platform lasted longer. GM launched the new GMT400 pickups in April 1987 as 1988 models, and the older trucks carried on under an R/V name. The Blazer, Suburban, crew cabs and heavier trucks stayed on the old architecture through the 1991 model year. That is why parts catalogs sometimes list a 1987 R10 or R1500 alongside the C10.

Year by year: reading the front end

• 1973 and 1974: the original front end.
• 1975: Chevrolet adopts a flush-mounted grille and GMC a six-segment grille. Chevrolet adds Scottsdale and Silverado trims, with Silverado as the new flagship.
• 1977: a second front revision with larger grille segments; power windows and power door locks become available.
• 1979: a minor update with dark gray grille bars and chrome trim around the turn signals.
• 1981: the big mid-cycle redesign. The sheet metal ahead of the windshield is reshaped, the hoodline drops and square headlights become standard.
• 1985: the last grille change under the C/K name.

Powertrains covered most of GM's catalog. The base engine at launch was the 250 cubic inch inline six, with a 292 six optional; a 262 cubic inch V6 replaced the 250 in 1985. V8s included the 307 (1973 only), the 350 and 454 from the start, a 400 added in 1975 and the 305 from 1977. Diesel buyers got the Oldsmobile 350 diesel V8 in 1978, replaced in 1982 by the 6.2 liter Detroit Diesel V8.

Underneath is a high-strength carbon steel ladder frame with a drop-center design, independent coil-spring front suspension on two-wheel-drive trucks, a live rear axle on multi-leaf springs, recirculating ball steering and front disc, rear drum brakes. Pickup wheelbases were 117.5 inches for the short bed and 131.5 inches for the long bed, with 164.5 inches for the crew cab.

Why they got hot

Several things line up. A long production run means plenty of trucks and plenty of parts, including reproduction sheet metal and trim from restoration suppliers. The body is flat and honest, which makes it a good canvas for anything from a factory-correct Cheyenne to a bagged shop truck. The chassis is simple and well understood. And the engine bay was designed around small-block and big-block V8s, which makes a modern LS swap far less painful than in many newer trucks.

Values reflect the demand, but they swing hard with condition, configuration and build quality. Hagerty's marketplace data shows how wide the range is: a 1981 K10 Custom Deluxe restomod with a 496 cubic inch engine sold for $35,578 in September 2025, while a modified 1984 K10 4x4 sold that same month for $9,898. Check current Hagerty valuation tools for the exact truck you are considering rather than relying on a single headline sale.

What to check before you buy

Rust decides most square body deals. Carolina Classic Trucks, a restoration parts specialist, lists the usual trouble zones:

• Cab corners
• Rocker panels
• Floor sections
• Lower fenders and wheel arches
• Door bottoms
• Bed supports and inner structure, especially on trucks that lived outdoors or in wet climates

The same source warns that rust hides under weatherstripping, in the floors and along lower body seams, and advises fixing metal before any cosmetic work, since solid metal makes panel alignment and sealing far easier. Mechanically, check brake hoses, seals, hardware and valves on trucks that have been sitting, and look for worn bushings, tired shocks, loose tie rods and old ball joints. Get under the truck and look at the frame rails as closely as you looked at the cab; a clean cab on a compromised frame is not a bargain.

One parts note: many pieces are shared between Chevrolet and GMC, but trim, badging, some interior parts and model-specific details differ, so confirm the application before ordering.

The common swaps

LS power

The square body is one of the friendlier LS platforms. In 2015 Holley and Hooker introduced a coordinated swap system for 1973 to 1987 two-wheel-drive C10 and C20 pickups, including engine brackets, a transmission crossmember, headers, exhaust, an oil pan and an accessory drive, all designed to work together for proper drivetrain geometry and clearance. That system was engineered around two-wheel-drive trucks, so four-wheel-drive owners should confirm fitment for their own setup. If you are pulling an engine from a salvage yard for the job, see our junkyard LS guide for engine codes and controller compatibility.

Dropping it

A static drop is the classic street truck move. A typical kit combines drop spindles and lowering coil springs up front with a rear flip kit. UMI Performance's 1973 to 1987 C10 kit, for example, drops the truck 4.5 inches in front and 6 inches in the rear using 2.5 inch drop spindles, 2 inch lowering springs and a flip kit, without notching the frame. UMI notes that its drop spindles need 1.25 inch thick brake rotors, while some 1981 to 1987 trucks came with 1 inch rotors, so plan for brake parts as well. Its fitment list includes the 1987 R10 and R1500, another reminder of the late-run name change.

Bagging it

Air suspension lets a truck lay on the ground at a show and ride at a usable height on the road. Ridetech, for example, sells front air spring and shock kits for 1973 to 1987 C10s designed to work with its own tubular lower control arms, sold separately. Fitment tables on these kits vary by year, cab and model, and Ridetech's own listing shows separate entries for 1973 and 1974 trucks, so match part numbers to your exact truck before ordering.

Whatever direction you take the truck, buy the best metal you can afford. Drivetrains and suspension bolt in. Cab corners do not.