The reprofile can be accomplished without CNC equipment. You would need to make a pivot fixture that holds the rocker. Finding out where to put the pivot is the issue so the fixture needs to be adjustable and repeatable.

The rocker pad ( where it contacts the cam ) should have somewhat of a crown, the goal is to move this crown towards the rocker pivot. If you can get a hold of come CAD software / Autocad Inventor you could get some idea of the effects.

Given the complexity of this rocker system, I'd first look into shortening the exhaust " Y " pipe to suit your rev range. For some reason, Euro and Japanese cars seem to like split manifolds on inline engines making what amounts to a tri - Y exhaust header.

Do you have access to a dyno? That is the only real way to determine power gains, anything else is a guess. ( unless you are testing by drag racing but even then there are variables. )