Use a table ban saw to hack off the 340 piston crown .

Dicer said
I know for a fact, really have you done this......no safety issues here

So a wood router and a metal milling bit is OK, I don't know where you're from but you need to stay there.

No, I have not personally done this, one of my friends did on a 3.9 V6 and it turned out great. It is a pity that you can't recognize the difference between an obvious safety hazard and an alternative method of doing something. In my four decades of working in power plants, if a machinist did something like that there would be a "coaching session" about work practices. Your avatar is appropriate but I fear you are showing the wrong end. I am through with you.