Francis-
Welcome aboard. Although I did not do the work, my rig has an early '70's Nova clip (also rear steer). Any of these GM X series cars will work and there are a lot of great parts available. Their width is pretty equal to the AD pickup frame. It is important to get the measurements correct before firing up the welder, so take your time.
If I had to do it again, I might go for the second generation, front steer. Better parts availability and less hassle with the steering components getting in the way. Lots of experience here at the Stovebolt.
Here are some photos:
PhatBoy Phrame Photos
