You should notice a definite increase in power, especially because of the better breathing heads and change of cam. Some of those smogger heads had pretty poor flow characteristics. If you use Vortec heads, you will have to use a new manifold as the bolt pattern is different. I am not a fan of adapters, so if you decide to use a different kind of head, I would get a new intake as well. The Edelbrock RPM manifold flows better than a stock GM aluminum manifold, and it would be money well spent.