[71Rat]

if your talking about the center one that goes into the crank. without air or a flexplate/flywheel to hold onto. put a ratchet on it and smack it sharply with a hammer or something hard. the sudden jerk(like an impact gun would cause) can sometimes break it lose. or you can try to put some cord into a spark plug hole and have the engine turn around untill its locked and then loosen the bolt

hope that helps, just ideas

71rat