I use a 3" diameter hole saw in a variable speed 1/2" drill motor on the pistons. Use lots or cutting oil and the piston cuts like warm butter. It cuts the piston crown away just inboard of the rings and frees up the crankshaft so it can turn. Those cast iron pistons are going to be junk anyway, as most anybody who would rebuild the engine is going to bore it and use aluminum replacement pistons.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!