A fellow poster here and friend of mine suggested that I post here with what I've done so far.
I recently picked up an old Astron Belt cab and have been working at cleaning it up and retrofitting it for use as a Jamma Cab and eventual MAME cab.
One thing that I wanted to do was to maintain as much of the original cabinet as I could. One of those areas was the coin door. I wanted to somehow add some buttons to it for credits, and noticed that there were the windows to either side of the coin slots that are used to illuminate the old 25 cents to play plates.
I found these low-profile pushbuttons on Suzo-Happ:
http://na.suzohapp.com/pushbuttons/5700044x.htmWith only minor filing on the cost to play plates, they fit perfectly into the coin door by pinning them between the coin door and the metal plates. Added a quick legend and a DPST switch inside the cabinet, and I ended up with the look in the photo (sorry for the fuzziness, bad camera and bad lighting when taken). Wired the buttons up for credits and can hit my DPST switch to turn off the function and require coins for credits.
Quite happy with the final look and was encouraged to post here for anyone else that might be looking for a way to retrofit the old Midway coin doors.