[EdHolland]

Here's my recreation for a 16X, based off one of the few pictures I could find and scaled carefully:

   

I gauged the holes at 1 3/8", spaced 2" apart. I cut the piece from hardboard which was spray painted black.

I've not settled on the material yet. I thought furniture underlining might work, but looking at your picture, something like canvas might be a better match. Our radio had lost its back completely before we found it.