7 1/4 rearend brakes swappable on to 8 3/4 ?

In short no. But depends on which 7 1/4 rear your talking about. They made big bolt pattern 7 1/4”, small bolt, 9 bolt rear cover, 10 bolt rear cover BBP which is a kinda hybrid rear. But no way will axles interchange. Brake Plates will work on a 8 3/4”.