Do you know what your real axle assembly came from? Custom made? A stock A-body 8 3/4 would have 10 X 1 3/4" brakes. If yours has the big bolt pattern and 11" brakes, there are 3 different backing plate possibilities. 11 X 2, 11 X 2 1/2, and 11 X 3. Each one uses different shoe hold-down pins, shoes, and drums. All the parts need to be for the same size shoes, and match the backing plate. You should be able to tell if there is a mismatch because the shoe friction surface won't be square with the backing plate. A 2" shoe on a 3" backing plate will be at an angle were the outer friction surface of the shoe will hit the drum when applied, whereas the inner surface (next to the backing plate) won't hit the drum.....at least not until lots of uneven wear happens. Other shoe/backing plate mismatches will result in the same type problems, sometimes reversed where the inner will hit and outer won't. There are a few combos that can't happen.....such as 3" shoes on a 2" backing plate. You just can't get the drum seated against the axle flange in that case. The easiest way to make sure is to use a framing square against the backing plate and shoes to see if they're sitting straight and square. I've seen a few drums that weren't cut correctly for the shoe it's made for, causing the edge of the shoe to rub on the vertical surface of the drum. It's a similar situation if you use a 3" brake shoe on a 2 1/2" backing plate/drum combo. Along with a cocked shoe problem, the shoe bottoms out in the drum and hits a section of drum that hasn't been machined.
