Needed to reinforce the transponder/radio face plate so I fabicated a couple of stiffeners. One wraps around the bottom of the transponder and ties into the radio side of the panel. A "pocket" was fabricated to bridge the faceplate to a vertical angle. The pocket will also serve to store charts or other small items.
Filed the transponder cutout for enough faceplate clearance to get the transponder in/out of its tray. The transponder faceplate is partially recessed in the panel.