The only differences outside of factory tolerances I'm aware of come from different axles. For example, a factory A-body 8 3/4" (SBP) has a different width than an A-body 7.25" (SBP) for the same year. And a factory BBP A-body 7.25" is different from both the SBP 7.25" and 8 3/4". The same is true for the '71 B-bodies for sure, the 8 3/4" and 8.25" are different widths too. A-body 8.25's are the same width as the BBP A-body 7.25's (or so close I can't tell the difference in measurements).
My own measurements have always shown the housing widths to be very close to the list at the beginning of this thread, I've measured half a dozen different 68-70 B-body axles and found they were all pretty much dead on, less than 1/16" different anyway which can easily be a measuring error if you're just using a tape measure. Same for the couple of E-body, A-body and C-body 8 3/4's I've had in my possession at one point or another. The big differences are all from different style rear axles. Obviously there is a factory tolerance on the housings themselves, but at least from what I've seen that tolerance is much tighter than anything related to the frames or body's on these cars.
