I built a 612 (4.530 x 4.750) in an Indy block with B-1 original heads 3 years ago. It lasted to about the 1000' mark on the first run and the cam broke! In conversation with another Mopar racer, he thought there might be a clearance problem with the rods and cam with a 4.75" stroke. Uhh ... maybe he has something there. Oh well it only cost me about $12,000 to find out. All I'm sayin' is you better check this out.
K.B.