I think the answer is they didn't. I've seen a lot that says they didn't use the same cars in both movies. They built 3 cars for Two Lane Blacktop, and all were built by the same people. They had two cars for American Grffiti. One to crash that was pretty stock, and the 2nd for all the show shots. If you watch AG in the end drag race scene, you'll see when it rolls over the '55 is a single exhaust car underneath, and not anything but stock suspension.My bad! I even have the 1/18th scale '55 sitting next to me! I get those mixed up all the time. I guess it's because I heard they used the same car for both movies. Don't know if that's true.