1970 Buick GS455 Sport Coupe with a built 455 and 4.10 posi, early bidding far under A-body 455 sales

Why we picked it

The seller has owned this GS455 for 40 years. The 455 was rebuilt .030 over with TA Performance Stage 2-style aluminum heads and intake, a roller cam, MSD ignition and ceramic-coated headers into a 3-inch dual exhaust, and the seller says it was overhauled about 1,000 miles ago. It backs up to a TH400 and a 4.10 posi rear, and already has front disc brakes, aftermarket rear lower control arms, a sway bar and double-adjustable shocks. It comes with a clean Arizona title, extra parts and the stock radio.

With 14 bids so far the high bid is $8,000, and the auction runs to Nov 12. Comparable modified GM A-body 455 coupes have sold for roughly $28,000 to $45,000 online this year, so there is a lot of room even if bidding climbs. The paint is an older (about 20-year-old) black repaint and the listing admits chassis and underbody rust, so budget for metal work before you count on the low end of that range.

The value check

The current bid is $9,000. Comparable cars in the same condition have sold for $28,000–$45,000, so the middle of the market is about $36,500. That put this car 75% under. Bids usually climb in the final hours, so the discount will likely shrink.

Modified, driver-grade 1970 GM A-body 455 coupes have recently sold online from the high $20,000s to the mid $40,000s, including a modified 455 Olds 442 Sports Coupe at $35,190 on Hagerty on Nov 2, 2026. The current $8,000 bid (about $8,560 with Hagerty's roughly 7% buyer fee) is about 77% under the $36,500 midpoint, but there are nine days left and bids usually climb.

Where the numbers come from:

• 1970 Oldsmobile 442 Sports Coupe, modified 455, sold $35,190 (Hagerty, Nov 2026)
• 1970 442 Holiday Coupe 455, sold $49,167 (Hagerty, Apr 2026)
• 1969 442 Holiday Coupe 400 auto, sold $26,750 (Hagerty, May 2026)
• 1970 Buick GS 455 coupe, 21k miles, rust at left rear wheel opening, Bring a Trailer Oct 2026 (reported as GBP 24,849 on The Classic Valuer)

What to check

• The listing notes chassis and underbody rust. Inspect the rear frame rails and kick-ups, trunk floor and drop-offs, lower quarters, and the rear window channel.
• The seller calls the body and chassis completely original while also saying it was restored about 20 years ago. Ask for photos of the floors and frame to settle it.
• The page does not say the 455 is the car's original engine. Ask for the block code and date.
• Mileage is listed as TMU (true mileage unknown), and the tires have old date codes, so plan on new tires before any hard driving.
• Hagerty adds a buyer fee to the hammer price, and bids usually climb near the close.

Making it drive like new

The drivetrain is already built, so put the money into the chassis and brakes. Boxed or tubular front control arms, a thicker front bar, poly bushings and a quick-ratio steering box will tighten up the soft A-body. Bigger front discs with a dual-diaphragm booster, rear disc brakes and a 200-4R or 4L80E overdrive would make the 4.10 gears livable on the highway, and a fuel tank and line refresh plus modern three-point belts are cheap safety upgrades.

6 builders make a complete chassis for the 1968–72 Chevelle, GTO & GM A-body. Compare them side by side, along with what it takes to stiffen the factory frame.