We used to build our race car engines like that. A 350 with 305 heads and a 2bbl. Rules stated we had to use OEM parts and a 2bbl. It upped the compression ratio and they ran fine. As far as Longboxes comment- I am not sure about newer Pontiac motors, but I know the older ones (70's) were not the same as Chevy despite being the same displacement. (ie. a Pontiac 400 and a Chevy 400 are not the same)
