Ok guys this seems to be a pretty common question so lets do a sticky on it
Question: What frame will fit my 68-72 convertible Chevelle?
Answer: Any frame from a 68-72 CONVERTIBLE A-body which means Chevelle, Cutlass, 442, Skylark, GS, GTO and LeMans. Hint- If you are buying a parts convertible for the frame then make sure it has a boxed frame! Some folks swapped out their hardtop frames with ragtop frames for racing.
Question: Can I use a 68-72 El Camino frame? They are boxed after all...
Answer: No you cannot just bolt one of those in. The section between the wheels (the boxed part) is longer by about 4".
Question: How about a hardtop frame?
Answer: Nope as it isn't boxed. IF you are good with a welder and the boxed part on your original frame isn't toast then you can cut out the boxed part and weld it in or you could try making your own boxes for it.
Now if someone else can fill in the 64-67 frame info it would be greatly appreciated.