Yes, if the .050 is indeed 262, that is way to much cam. That cam could get you 8k rpm, if the heads are big enough. You should be able to get 375 hp with a 232 cam.
The 289HP heads don't have any flow advantage, unported, they just have spring seats and screw in studs. Porting isn't easy on them either. Stock they flow about 165 and the best porters can't get above 240 cfm. I had a set of C6 heads and after quite a while porting on the intake, schooled by a pro, I was only able to get 196 cfm with a 1.90 valve, good for close to 400 hp.
A EMC competitor, got 2nd place, in the last EMC with 294 ci, 235 cfm heads, dual plane intake and a 242@.050 roller cam for 440 hp @ 7.2k.