I think the heat/freezing thing may have been a dead end. With oil in the sump heat transfer would have nullified any effect?? Probably just as well warming the motor up.
Did you try the heat/freeze combo? if not then def worth a try, it's amazin how a bit of heat can loosen stuff off. Although I would have thought a decent twatting with the ammer would've worked. Incidentally Aluminium expands/contracts almost twice as much as steel for a given temp.
In any case if ya use a naked flame just 'be prepared' (yeah I know prob goes without saying) and make sure your camera is rolling first just in case.