Heat's definitely a good way to try it to see if it will move at all.
I'd lay it on it's side and make a good support for the stand near the pivot so that when you drift it the load passes through the stand rather than the frame tabs, I usually use bits of old railway sleeper for this sort of support as it is solid but doesn't usually damage the metal.
You could try one of those hammer drills that you can turn off rotation to give drive to a drift with some small shock force as opposed to itting-wiv-a-big-ammer method.
