Ok, here's what I ended up doing. I needed to drill out the plug almost all the way through with a 3/8" bit. I also had a rearward clearance issue (riveted in cross member behind the torsion bar crossmember) so I had to cut the bit down with a grinder. I took about half an inch off the chuck end (just enough to be held by the chuck) and cut the front end off flush. It cut good enough with a 90 deg point, the metal was soft. Also, I needed to use a right angle air drill (again clearance issue).
Once drilled through, I used a Hanson Multi Spline extractor. It finally bit solid enough that I new it wouldn't strip. Heated up the case around the plug with the MAP/propane torch till it started to smoke; slow increasing pressure with the 18" breaker and finally it broke free. Plug went up on the "wall of shame."
Hope this is helpful for someone else in the same situation.