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

Jessearent said

You got an outside micrometer 4" - 5" you can trade even?

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This is what I use to hold pistons I’m grinding on. To get them tightened up properly put a set of Vice grips on the barrel and it gives you more torque (that word excites me) to hold the piston so I won’t move.