worst case scenario, you can always make a back door out of plywood... might be able to find one at a pin show fleamarket?
paint templates don't exist for em games, so you'll have to make your own... since you are handy with graphic arts, that's doable... there are a few threads on how to make templates, and clay has info on how to do them on the pinrepair site... www.pinrepair.com
you can probably remove the blue paint, and with any kind of luck, the original paint is still there underneath the blue...
there's also info on clay's site about how to properly repaint a cabinet...
cool game, and good luck... pics please! we like pics here...