I made the "L" bracket with piece of flat galvanized steel 1.25" W x 1/16" thick & bent it into the "L" shape in a vise. Then drilled hole for attachment to the radio. For the spring steel that clips to the firewall flange, I used a houshold window spring clip made to repair old windows that slips into the window side channels. Steel & spring clip purchased at local True Value hardware store. I had to cut the length of the spring clip & then drilled two holes, side by side, & attached it to the 'L" bracket. I did this several years ago & now not able to give exact measurements. I wish I had made a pic of it.
Regards, Paul '63 230SL