for those that don't know, we've been running rpm heads and a flat tappet cam for a few years. it's been fun working the old e-heads. i was told you couldn't run 5's with a big block and e-heads, but i did that a couple yrs back. sat. it went 5.91 a couple times at over 115mph. NOW...... the dilema: i have a chance to get a set of -1's that was ported by hensley {i think}. or, just do some welding and more epoxy on the rpm's and see if i can get any more out of them.

A rough idea could be to compare head flow in the area under the lift that your present heads flow at, and look at the same area under the lift that the new heads flow at. You can expect that a decent build will produce about the same hp per cfm, given many variables are close. That would also assume you can deal with the hp coming in at a higher rpm.
Wait, just maybe toooo many assumptions there.
My experience- best Corrected ET unported 440-1 heads, 9.24 at 145 mph, at 3000 lbs. (actual, 9.34, 1650 DA)
Ported, 8.779, 3,000 lbs, corrected came out at 8.63.
Every build will vary.