B body rear brakes onto A body axle

Yes you could but why when new is at the store?......

Just pointing out a possible option here.

................. The original studs were 7/16". When I check the amount of meat left on the flange, going to the 1/2" studs would leave little meat between the original 4" circle stud holes and the new 4.5" circle stud holes.

Using pressed or screw in? 1/2" screw in studs have worked well in mine.