Stuck pistons/Crank, any ideas?

I'm not sure what your budget is or what you plan on doing with the engine, but if it was sitting outside and exposed you may want to consider finding a better core to start with. I've gotten involved with rusted motors twice and both times was a disaster. Cast iron loves to rot when exposed and the cylinder walls may be pitted badly enough to not be able to be cleaned up by boring the block. I'll never waste my time and money on a rusted/seized motor again. Its cheaper, better and easyer to start with a core that was under a closed hood with the air cleaner on it.