If the engine is realy locked I wouldn't use a wrench on the crank bolt . Some people get over zellious and you could break it off . A better way is a strap wrench around the crank pully. As Don said coat the cylinder walls with WD-40 or some good penitrating oil. Let it set a while then try turning it over. Maybe you could hook up a starter to it and leave the plugs out while trying to turn it. Anyway try to get a better price as hes the one that let it sit with no protection.