I have a 1968 GTO, and would like a new frame for it. What year of cars will work for it, and what GM models. 68-72 Are they exactly the same??? Help

Hollander shows 68-70 Buick Special (exc GS) and 68-70 Olds F85.
that's the short list.
Take a look on the frame by the left rear wheel and see if there's a P/N stamped -shown as manufacturer's id and date.
http://www.chevellestuff.com/qd/images/frame.jpghttp://www.chevellestuff.com/qd/images/parish_1121692.jpg
There may be more than I listed.

I am thinking that the Pontiac is 2 inches longer then a Chevelle

I did a body swap on my stock car in the 70s, I pulled off the GTO body ('64) and swapped on a '66 Chevelle body. And that's exactly what I found, that the Pontiac frame was about 2" longer then the Chevy was. For my application it was no problem, but for a steet car it would be more of an issue.

A friend put a 1971 Olds Cutlass frame under a 1969 GTO. No problems.

The only difference in the 68 A-body frames that I can remember is the extra guard located in the center of the crossmember. I've never seen a 69-72 with this guard. It's just a V-shaped piece of metal added.
I'll check my buddys 68 Velle tomorrow to see if it has it.
I parted a 68 442 that had it.
I would think all 68-72 GM a-body 2 door hdtp frames exchange.

The only difference in the 68 A-body frames that I can remember is the extra guard located in the center of the crossmember. I would think all 68-72 GM a-body 2 door hdtp frames exchange.

I always thought all 68-72 A-body frames were the same, with the only minor exception being this extra piece on the front crossmember. My 68 Chevelle had it, and I replaced it with a frame from a 68 Cutlass with it

Make sure you get a 2dr frame... elcamino, wagon, and 4drs are longer wheelbase