Where the 8 3/4 fails is pinion gear deflection inside the housing. So diameter at the flange is irrelevant, it doesn't deflect there.
If you really have 550hp and excellent traction you might have a problem and no back brace will handle the pinion deflection. All a back brace does is add extra unsprung weight here, which is exactly what you do not want in a handler. Now if you want to clean up the housing and make sure the tubes are fully welded and straight then that's fine.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
