bbp axle change what backing plates are needed

I bought mine from Moser, first thing they asked, was if I wanted A-body offset, or B-body offset.
I bought the A-body offset axles, which allowed me to keep my original backing plates, brakes, and drums. Just had to redrill the drum for the bigger 5-lug pattern.

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This is exactly correct. I bought mine from Moser as well. On the phone they asked three questions:

1) What brakes will you be using A body or B Body?
2) What year is your car?
3) What rear is in it?

My axles fit perfectly the first time. I used the B Body 10"X1 3/4" brakes, the backing plates, drums and hardware all came off the same car and they fit like a glove.