There still isn't a decent block to use with a smallblock head that's over 300cfm, so why bother?

R.

To the OP: Your stock heads flow no better than 228cfm stock, and that's the best port. There's a 100hp potential in a set of Stealths, or Sidewinders which seem to the the latest and best budget head, or the ProComps, or the Edelbrocks even the street ones.
Performer RPM intake should be on your list as well.