[dsraven]

wow, looks like a fun time.

what has worked for me in the past is to heat the area some, give the plug a rap or 2 with a hammer and walk away. when it cools off the plug will sometimes give.
another thing I have done that usually works every time is to weld a large nut onto the plug. large enough so you can easily weld inside the threaded area of the nut. in this case I think the plug may have a flange on it so don't weld to that area so a slightly smaller nut would be in order. start the weld on the plug and ensure you follow the weld around the inside of the nut keeping the plug in the weld puddle for max heat and penetration onto the plug. the heat from welding expands the plug and seems to break the corrosion bond between the metals as they heat and expand then cool and contract at different rates. let it cool off completely and then try turning the nut you welded on. this idea also works well for removing a bearing race inside a housing. weld a bead around the inside of the bearing race but ensure not to touch the housing. turn the housing over before you walk away and when you come back sometimes the race is sitting on the floor because it shrunk so much it actually fell out of the housing bore.
anyway, glad you got it out and can carry on.