The MA BB was a RB, 4.15 stroke. It started with ported Ed heads later got EZ's. As I rememember it was dynoed at around 600 HP with the Ed heads.

On B vs RB I like and run the B. That said, if you run more than 3.75 stroke, rod ratio and piston height can be greater with the RB and that can help with durability at sustained high RPM.