i have beat on several 741's, [3.91 & 4.10] that i got from /6 trucks and vans that had sure grips, without problem number one. all the pinions neck down to the same diameter at the flange, so not being a rear gear expert by any means, i really don't give it much thought.
also, i have only been at 425/435hp, so for an extra 100hp or so, maybe use a brace on the housing ? i never have done that, but if i would, i'd go clear to the backing plates, using inserted tubes for the u-bolts.
subframe connectors help at any level, tightening up the car a lot. don't know if this helps or not. i'm sure you will have other responses different than mine. luck to you !