With not enough real estate left on the instrument sub-panel, I had to come up with another idea for mounting of the two AoA control boxes.
The picture below shows my initial idea. I made up two aluminium angle braces that go from the firewall to the sub-panel, and to these I will attach another larger aluminum angle bracket which will hold the main control box. Future access will need to be from underneath, but at least it won't be right back on the firewall, and will be hanging down lower than the sub-panel (but still high enough so that my feet won't hit it).
I'll think of how to mount the second control box later, but my initial thoughts are to add a hinged panel as this box has a few control dials that need to be accessed when setting up the flap position.
I've drilled lightening holes in the large angle, and alodined and primed the parts ready to assemble tomorrow.