If it's in regards to the 1 or 2 pc rear, I've always run the 1 pc rear on my E bodies, I suspect the 2 pc rear is for shipping purposes?, the 1 piece rear comes folded in half for shipping (easily straightened)

If you got nothing on your car, you'll need to determine what kit will fit your current drum/rotor and master/booster set up, and frame over or under front lines, generally I find 71's are frame over, and 70's are frame under, but there's so many variables plant to plant, year to year