I have 3 differnt 8 3/4 rears that I have took the axles out and wife has helped me by moving them. I have a e body. A 71 b body. And a 73/74 b body
I know wich housing is wich. But not sure wich pair of axle go to the housings. So I need some help.....housings are bare

The specs might be in the archives. You could also mockup the axles and I think with the right axles in the right housing you want 1.5" between the ends of the axle splines. Add a bit for what you get for gap for the backing plate/foam/steel gaskets thicknesses & want 1.5" or to k.i.s.s. just slam the brake assy's together with the axles & measure the end gap there in the middle & likely you'll either be close to 1.5 or way off so it shouldn't be hard to get em matched

Aren't all three of those the same width I have been warned about swapping axles form side to side, it is a reaaly big NO NO, according to Mark Williams Make sure that all three adjsuters end up on the passenger sides

Its like putting used T-bars on the wrong side...your twisting them in the opposite direction they're used to.

Ahhh gotcha that makes perfect sense