I think we might not be getting the whole picture here, earlier he said he could stand underneath it and almost touch the top of the tree with his bar.
That tell me it's almost on the ground so i wouldn't sweat it, i wouldn't under cut it if it's that heavy and that close to the ground , use the proceedure i talked about earlier ,or hire a proffesional,or irrigate the crap out of the stump untill the tree does come all the way down what do you think of that idea, run water into the ground for a couple of days untill it falls over that might save you a couple of buck.
If you are going to keep thinking about this you should ribbon off a no work zone for the danger area underneath that tree so that someone doesn't get hurt.