10 x 2 1/2 SBP Drum

To further muck up the works...the 7.25 and 8.75 small bolt pattern backing plates arent interchangeable.
They are axle specific, different offsets.
Best bet all round is to go with aftermarket large bolt pattern axles compatible with the 10x2.5 (or larger drum) brake assembly offset.

Why Chrysler made the 72 and older A body rear brakes the way they did...well, my only thought is it had to be cheaper.