Difference in drum brakes A-B Body

It doesn't matter what body style the drums came from. The backing plates are different from 1 3/4" to 2 1/2" drums, the bolt pattern you already know.
The offset is built into the backing plate.
There is also differences in drum diameters, 10"-11".


My understanding ( I haven't tried this) that backing plates from 8 1/4" will also bolt in.

Hope this helps.