1980 Chevrolet K5 Blazer with a 427 big-block swap, driver quality

Why we picked it

Why we picked it: big-block power is a common goal for K5 builds, and this one already has a 427 V8 in place of the original engine, with an electric fuel pump and an electric radiator fan. The dealer describes it as a good driver-quality Blazer with a good interior, upgraded high-back bucket seats, new valve cover gaskets and a new rear window motor.

At $16,050 (after the dealer's discount and doc fee) it sits about 22% below the middle of what comparable driver K5s have sold for. It has been repainted from light blue to dark blue in an older paint job with imperfections, and there is rust at the rear wheel wells.

The value check

The seller is asking $16,050. Comparable cars in the same condition have sold for $13,200–$28,000, so the middle of the market is about $20,600. That put this car 22% under.

Driver-grade 1976-81 K5 Blazers with flaws sold for about $13k-$28k over the last few months; clean Cheyennes brought $35k and up and were left out.

Where the numbers come from:

• 1978 K5 Blazer, Barrett-Jackson, $13,200 (Sep 2026)
• 1981 K5 Silverado, Hemmings, $15,250 (Jul 2026)
• 1981 K5 Blazer modified, BaT, $18,250 (Aug 2026)
• 1980 K5 Blazer, BaT, $22,000 (Jul 2026)
• 1978 K5 Cheyenne, Mecum, $27,500 (Sep 2026)
• 1976 K5 Cheyenne, Cars & Bids, $28,000 (Aug 2026)

What to check

• Ask for proof of what the 427 is (casting numbers, build records) and whether the transmission and transfer case were upgraded to handle it
• The dealer notes rust at the rear wheel wells; check rockers, cab corners, the tailgate and the floors as well
• The engine swap means it is not original, so collector buyers will pay less; value it as a builder
• Title status and true mileage are not stated; sold as-is with a 3-day return option (buyer pays shipping both ways plus a $1,000 restocking fee)
• The dealer page shows two addresses (Brookings and White, SD); confirm where the truck is

Making it drive like new

With big-block torque, prioritize brakes (hydroboost and larger front discs), a cooling-system check, a TH400 and a fresh transfer case if not already done, a modern steering box with a frame brace, and new springs and shocks before adding larger tires.

3 builders make a complete chassis for the 1973–91 K5 Blazer, second generation. Compare them side by side, along with what it takes to stiffen the factory frame.