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

Jesse, what 340 pistons do you have/have access to? If you haven't read about what was referred to as the Hoover engine look here... 340 pistons in a 360?
Back in the 70's Tom Hoover use to use 8.5-1 340 pistons in 360's... Apparently you take .030 off the top, chamfer the edge & it may need valve reliefs cut depending on cam selection... There was also mention of possible having to relieve the back side of the pin boss to clear the crankshaft counterweights....

That's allot more involved that just a shave off the top... You probably would be hugely money ahead to track down a set of 360 pistons with a decent compression height...