7 1/4 is the only A-body rear available in both big and small bolt pattern from the factory
8 1/4 all came big bolt, and 8 3/4 A-body rear's all came small bolt
the difference between the big and small bolt 7 1/4 rear's is in the with of the brakes, I have read that in order to allow for the wider brakes the factory narrowed the housing