[olddog]

I guess it all depends on how good a job was done porting you current heads. If they were done very well, they may actually flow better than most heads out of the box. Odds are they were not ported that well, but you never know until you test them.

What type of power are you making now, with what engine combo, and how much more are you wanting or expecting?

EDIT:
If this is the 427W at 500+ Hp, I would say the heads are flowing pretty good. You could easily do worse. If you want much more than this, go BB naturally asperated or supercharge this engine, as it is.