Seems like I made it too hard on myself. On my second go at it I got it first crack, not exactly sure where I went wrong initially. I have it running with the latest raspbian 32bit build on Rpi4, simply double clicking on the file in the GUI after making it executable.
One thing to note... the Rpi is not happy if you hook up a 100c unless you turn off USB charging. I tried several USB supplies including a 65W PD supply that runs a 15" laptop to power the Pi to no avail. I settled for disabling USB charging on the mod in the end.
The eventual project here is to make a portable "tablet" for Escribe. I currently have a 7" touch panel with a Rpi mounted to the back. Eventually to be battery powered and a enclosure 3D printed for the back of the panel to cover the Pi. Why? I dunno, why not.
EDIT: may have spoken too soon, it appears to be crashing on loading any of my mods... investigating