The motor should turn a fraction even if the crank bearings are shot or the chain broken, unless the rings are stuck to the bore. I'd mix some acetone and dexron and squirt it in the plug holes and let it soak overnight, and repeat the next day, then try to break it loose at the crank bolt, CW rotation only. Also try with the starter and wrench at the same time (ratchet ONLY for this one for obvious reasons). Try with starter and wrench and smack the wrench with a BFH. If all this fails, pull the head off and use a fat stick on top of the piston and a BFH to break the rings loose.