Try this, take it out for a ride to get the engine and oil hot. While it is hot see if you can back off the oil drain plug then. I wouldn't recommend using any other method to heat up the plug. If the PO used something like Lok-Tite, you may be in for one of those self tapping drain plugs if your threads are damaged.... either that or a helicoil insert. Backing it off with an impact gun might be the only way to do it though. I would start by using one of those Dewalt 1/4" drive battery powered guns and if that didn't work, try the next step up... Regardless, I agree with you about the PO's intellectual gift rating.... Right up there with Mortimer Snerd.....