Wedge two large screwdrivers 180 degrees apart between the crankcase and the flywheel, putting some pressure against the flywheel. Don't get crazy and damage the case, just get some firm pressure going from two sides. Then screw the nut fully onto the shaft so you don't wreck the threads, and give the end of the crank a fairly good whack with a hammer. It should pop right off. If it doesn't, heat the center of the flywheel up real well with your Monokote heat gun, and try it again.

AV8TOR