Started cutting holes in left hand panel blank. Used a cutting wheel on a die grinder to cut the square one, after drilling out the corners. Worked very well just as it did on center panel. A light dressing with a square file and flat file and a very precise hole is the result.
Used fly cutter for the round holes. Clamped a piece of angle stock as a pilot hole guide. Practiced whole procedure on scrap, then drilled the four holes.
Amazingly, 2.25" holes are not all the same. The UMA pneumatics are one size, the ADI and TT Autopilot another. Will require some additonal filing to get the larger ones to fit. Hope I can trust the mounting holes.