Next step of the process was to match drill the inboard attach angle, the mount tube, and the backing plate. I set the tray and mount tube back into the airplane and measured the bolt locations once again to confirm that all was good to go.
Next I marked the locations that I determined on my mount sketch to work without interferring with anything forseeable. Then I took the tube and attaching angle and set them on my mill machine. I set it all up square and clamped it to the table. I drilled the hole for the #4 bolts about .015 smaller than 1/4 inch and then final drilled with the 1/4 inch drill. I knew I would have to manually drill the rivet holes in the backplate so I wanted the .250 hole to be as accurate in diameter as possible. It worked out great and the dowel pin that I had slipped in nicely.
After disassembly of the tube and the backing plate, I deburred all the parts. Next I made a little fixture from a block of aluminum for the dowel pin and a 3/32 pin for drilling the nutplates. It all worked like a champ.(cont in next post)