How to remove the Crank bolt on an Automatic Z with head off?

Renting an electric impact proved to be fruitless. I gave up on looking for pieces to bolt down to hold the piston down, so I ended up jamming a breaker bar to the ground and cranking the engine with the starter - messed up a tensioner spring in the process. Maybe not the best way to do it, but now I'm ready to clean parts and start re-assembly. Thanks for the help guys!