Hey Doug, cheer up, not sure if you have run a large stump grinder yet, but your BH is extremely safe in comparison to them
I hope we are not discouraging you, just trying to warn you of potential problems that some of us have encountered.
I use to hang window bars for folks, I get all done hanging these bars, and reach up and grab them and pull, just to make sure they were real secure, and the whole wall leaned out towards me................ Seems the brick mason had not used any brick tie.............. Did not fall, but you want to talk about scared.
Just trying to present some insight to keep from costly mistakes, not that you cannot do it, maybe more just as "be aware" of the possibility, and this is how we would handle similar situations.
And in the FWIW catagory, we just did a job just like what you are looking at, and stump ground them out, and the stump grinder did not get everything, but still succeeded in removing the irrigation system
Sometimes it goes that way.