The specifics of converting an E Body 8 3/4 rear end housing to an A body 8 3/4 rear end houseing

Once you have to narrow an 8.75 it's all the same, whether you want to chop it down to run 15" wide tires inside the wheel wells or if you want to convert an B/C/E body into an A body. Basically you're going to look at that list and cut it down the the specs needed for an A body. Then you're going to need a jig to put it back together that has a rod that goes all the way through from one side to another and through. It's impossible to put it backtogether (correctly) without a proper jig. It's not an easy job, but not impossible for someone to do at home.
As for axles, spring perches and other odds and bits go to Dr. Diff. I got my bbp axles there and I have always been super happy with their service