My speedo has been posted off to my instrument restorer. I wish I had taken better photo's of it, especially from the rear. The bezel crimp looks like it has never been disturbed. There is an opening at the back of the can, on the side, it is about 1/2 inch wide x 1 inch high, and there is holes tapped either side for screws to hold down a cover plate. Thats what it looks like. If my small memory serves me right the the face is illuminated from the external dash base bulb through suitably placed long horizontal slits in the can. I can't remember exactly, I'll need to post pictures now after it is restored.