I would suggest not modding the cabinet, just make a new control panel. If you remove the old control panel and leave the original wiring intact, you will be able to reverse any changes made if you are able to sell the machine. Easier said than done if you want to add joysticks and more buttons, though.
The scrolling sign would be really cool if you were able to control that with a serial or parallel port connection.
Good luck with your project.