I did some cleanup work. On some of the longer dead stumps (shown in the original picture), there was very soft pulpy wood throughout the heart wood. I could scrap most of it out with a hand tool and then clean up the rest with a brush on a dremel. The fungus itself was very superficial though. Lower down on the trunk, I removed bark that had fungus but it was overlying deadwood. All that fungus was contained in the bark. I then applied some lime sulfur as an initial clean up. It was overall pretty superficial clean up work.
I did realize though that there is a huge hollow core which I will have to figure out how to attack. Likely when I repot, I will need to open up a larger hole on the bottom or back side to get access. For reference, it is the large grey oak I have on
this thread.