Disappointed with my engine

I think it is 90% with your heads. With those internal parts, you should be well over 300HP.
Imagine this. Let's say you have a 500+HP 383. It runs great and you are happy with it. It has good Edelbrock heads that have been ported. So what would happen if you pulled those heads and put on the crappiest 383 heads there are; something out of a 383 2 barrel station wagon with small valves and crappy breathing. How do you think it would run? I could be wrong, but "crappy" small valve J heads are not helping.