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

Ironracer said
Just lay em back to a board to square em up, if you use masons line in the box, you'll get a tighter line. That's how I do it if it was a pallet stack of 2x4s... then just keep cutting

....or just lay the pistons in between palings on the pallet, and free-hand cut them with a circular saw.

Make sure to use the correct blade.