Valve to piston clearance

just for info, here's the cutters I mentioned:
Isky Piston Notching Cutters PNT-218

I've done it this way before. It's very time consuming but, you're ensured the 'eyebrows' will be in the correct spot, cause even changing head gasket thickness will change the location slightly.
If your pistons have existing valve reliefs, it's easier to stick the pistons in a piston vise and re-flycut them. I've done both ways.
The problem with these cutters is that they're probably too small for your application, depending on your valve size, of coarse. The relief needs to be at least .080 larger than the valve diameter, the parameter of the relief is as important as the depth.
So, with say a Ferrea 2.14, the Isky cutter will have to be at least 2.22" dia. So there's a limit to their use..