What heads do you have now?
Look at your casting numbers.
If your head casting numbers end in 049, or 781, then you have some awesome GM factory heads capable of 700+ HP with port work, and larger valves with a hyd roller on 496ci.
I am making 550hp on 049s with stock ports, intake gasket match, 2.19in/1.88ex valves, and a solid flat tappet cam on 461ci.