So better late than never, right?
I got busy with life and just now got the bus running again after parking it upon returning home after the fiasco shared in the thread.
We moved to a farm, so I literally had to get it moved.
I started with the ICP sensor as mentioned earlier. It started right up and drove to its new home with no issue.
I will update again in a few years
Edit: Just to be clear, other than charging the existing batteries and standard fluid stuff, I didn’t do anything but the injection control pressure sensor which was indicated by the code it was throwing.