Now that I have the panel cutout, it's time put something in it. At this time I only have my 300XL GPS/Comm and a GTX327 xponder on hand - thank you Gulf Coast Avionics. I test fit the radios and everything looks good. I then cut some aluminum angle I had on hand to attach the front of the racks to the panel (see pic 3). Ran out of time before I could start marking and drilling the screw holes for the racks and the rivet holes for the panel.
From the front
From the back
Attach angles. These will rivet to the panel and screw to the rack perpendicular to the panel