Would the bb C heads be better vs a set of 7a sb heads on a 403 rebuild? Will be using KB pistons on rebuild.

 

Assuming you can run an intake like a Performer RPM that has enough meat to port-match to the larger BBO intake ports, yes (the RPM won't allow the shaker scoop to clear on a 403 T/A, for example). As people are probably tired of hearing me say, the 400 BBO used C heads and the 403 flows just as much air. Why restrict it with SBO ports? Obviously you need to select the correct pistons to get to the CR you want due to the larger BBO chambers.

 

With the KB 6cc dish pistons, you will have right around 9.6 to 1. The 7A heads will give 10.6 to 1, too high.