best cylinder head

Valvesprings can loose a bunch of strenght over time and that can show up as loss of power without valvefloat, but if they are new and they are set at the correct height thats probably not a a problem.
Are your heads ported?
And do you get full throttleopening at the carb?
These are the real questions,since airflow thru the heads will be part of how high you can effectivle turn that engine and make some power and the second question is just something worth checking,its a very comon misstake.
Also regarding the comments that those heads wont flow well enough at maxlift,consider that the valve wont hang at full lift for very long and on top of that i doubt you will see anywhere near a true .650"lift at the valves after lash and that screwed up lifterangle us smallblockpeople are all blessed with add alittle deflection to the pushrods and you are probably closer to .615" or so at the valve.

Its not that i dont understand that you may want a better head on that thing i just think it would be nice if you made that thing run as good as it should before you go to the next level.
I think a W2 topend on that thing would be awsome but better to figure out the basics first.