Here's what a finished piston looks like. We ground the reliefs deep enough that we could switch to 1.6:1 rockers and still have clearance. Even so, the nastiest cut was only 0.075 deeper than the top of the piston. That's less than 5/64 inch, if it makes you feel any better in those terms. It was scary work, and it took a bunch of time and patience to double-check every valve, but it was worth it.