Which A-body do you have? Makes a difference. The Dusters/Demons/Dart Sports and Barracuda’s are 1” wider in the quarters than Darts/Scamps/Valiants are, so a wider rear axle works better in the sport body’s than it does in the hardtops.
I have a 68-70 B body 8 3/4 in my Duster, for example. It also depends on what wheels you want to run, higher backspace wheels are easier to find “off the shelf” in 17’s and 18’s than they are in 14/15’s.
As for the measurements, he probably just used a different landmark. The width of the drums does not change the width of the rear end from wheel mounting surface to wheel mounting surface. The offset on the backing plates is different, the axles themselves are the same. So either he screwed up his measurements or that axle is not a 65-67 B.
