Discovered 1 owner LS6...need rough value.....

I unearthed a local 1 owner '70 LS6 Chevelle tonight. The car is a local car (Hechler Chevrolet), and is still with the original owner. I had heard about the car, and finally got a chance to inspect it. It is an Atlanta car, built 12C, and still has VIN label attached to drivers door showing 12/69. It is a Autumn Gold car with black vinyl top and black stripes, saddle buckets. The car is a 4spd, cowl induction, console, posi, 4:10, am radio, gauges, and power steering coupe. It has been repainted once, wears the original top (showing a lot of wear), and original interior. The good news is it is a matching numbers car, with most matching engine components (headers, no smog, incorrect carb, and manifold, missing CI air cleaner). It has the original trans (incorrect shifter), and original rear with dated gears (didn't open rear). The other good news is POP, more than likely a buildsheet still in car, and original sales contract and many original dealership pieces of paper. The car was street dragged (has bolt on ladder bars), and doesn't appear to have been hurt (still has original sheetmetal w/ no damage to quarter wheelhouses..) The car has typical GM rust and rust around windshield under top. The owner was told car is worth around $17,500, and as of right now doesn't know if he wants to sell. My question is does this sound inline with what you (figured I'd ask some more advanced collectors) would expect to pay? Just trying to get a ballpark idea. I'm figuring on car needing 30-40k to certify.