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

Rat Bastid, how do you hold the piston skirts in a three jaw chuck without damaging them or even worse braking the skirts by tightening the chuck. and if you do not tighten it the piston will move around damaging it. Now it appears you have a lot more intelligence so tell me how you do it?

Long soft jaws. Pretty simple.