You can remove the nut that holds the arm on... that's how I got the locks off the coin door, and the coin box door...
take out your pcb, remove the pcb tray, and you'll see the coin box area encased in metal. If you take out the screw and two nuts holding the metal 'collar' around the front of the coin box, you can manuever a small socket wrench in there to remove the nut. Inside my coin box was another coin mech, the manual to the Capcom Impress (in Japanese, not much use), and some pricing stickers to go next to the coin slot (all in Yen, lol).