Originally Posted by MouseFink
Install a camshaft with .550” valve lift.
That won't change valve-to-piston clearance one bit, so that is really poor advice
Piston is nearly half way down the cylinder and heading away when the intake valve reaches full lift, no where near the piston at all.
Valve-to-piston collisions happen on the overlap period neat TDC, when the exhaust is just coming to fully closed, the intake is just starting to open, and the piston is just reaching TDC overlap ready to head back down drawing in mixture. All three parts are close to each other in the same small space.
Checking points are between 20° before TDC and 10° after TDC, check every 5° to find the closest point to the intake valve, then check a few degrees either side of that 5° interval to find actual clearance in the assembly.
As far as power, if your 781's are basically stock, no porting, only a 3 angle valve job.... then according to the Head's flow numbers for up to and at your cam lift it could pick up 75-100HP.
For valve to piston clearance mods I the block, you can rent a flycutting tool from Isky, you can carefully free hand it with a Dremel if it is diameter and not depth contact, or of it is just intake depth clearance you can retard the cam as this increases intake clearance and decreases exhaust.
I have also seen where guys have taken an old or spare valve and cut the face using a cut=off disc in a Dremel to resemble a milling cutter and use that like the Isky in-head tool, or solder a small piece of high speed steel or carbide cutting bit to a old valve face and carefully cut with that down in through the installed head using the valve guide as a locator.
Piston Notching Cutter Tool : ISKY Racing Cams, Do It Right
We had a member here, I haven't seen him post in a while, BobCRman, who had used several sets of those heads and never had any problems with them.