7 1/4 rear

A lot of the measurements you'll find are from the housing flange to housing flange, and don't include the length that the axles stick out past the flanges. With the brake support plates (backing plates) mounted, it's hard to measure that distance, so instead I'm measuring the distance between the surfaces where the drums mount over the studs. On the link I posted above, look under "Rear end widths, drum to drum." You'll see 57 1/8" for the A-body.

As for the stud spacing, I have the small bolt pattern that all A-bodies had until 1973. "Small" means the studs are in a circle with 4" radius. Look around for how to measure bolt pattern.