Add some heat into the mix after you drain the pb fluid. You could also just plan on replacing your crank. I am not too familiar with the 505 engines but you should be able to find a new one. If you can find a new crank you could just cut the old one off at the con rod and the will allow you to remove the jug from the rest of the engine. Or even just split the cases and remove the crank without cutting.
Just my first thoughts if the jug is un willing to come loose from the piston. Heat before destroying though.