I don't suppose there would need to be much difference. Just add a debounce circuit to the Cherry microswitch in a standard coin mech and wire the START button to it. Perhaps hack the rom to say INSERT COIN instead of PRESS START (same number of letters). The only downside is your game would start as soon as you drop a coin, and additional coins would be ignored. Ideally a counter circuit and LED display on the panel would track coin drops and presses of the panel mounted START button. In this case, the ROM would need no mods at all, any single player game that launches with the START button could be put into coin-op service.
I'm going to try to build a custom theme for just my favorite arcade games (just the MAME games I remember the most in my local arcade from the 80s). Its a bit different than "favorites" because I don't want gameboy, SNES, etc.
Definitely not over 255 characters - and the folder name is currently "-CLICK-HERE-FOR-EVERY-GENESIS-GAME-" (with dashes in the beginning and the end) and it works fine. I wonder what caused it (and on 3 different folders, on 2 separate Pi setups I wasn't able to play any games inside those folders).
