The top of the control deck just lifts up.  I put a few blocks of wood to hold it in place when it's down (it has a snug fit).  The main card on the left is an I-PAC⁴.  This baby almost has enough inputs for every switch I put on the game, and it turn just plugs directly into either the USB or PS/2 keyboard port.   It works great. 

I also got its sister card the Opti-PAC for hooking up the trackball and spinner.  It too is great, and you can also connect 2 more buttons (mouse left & right) which I used so the trackball can double as a mouse for running windows.  These last two inputs also got me enough inputs for all the buttons I wanted :^)   Again, this card simple turns these things into a serial mouse.   No extra software drivers are needed with either the I-PAC⁴ or Opti-PAC - windows just ran them.   I should note that the Opit-PAC allows for controlling 2 sets of trackballs, spinners, and buttons.  I am only using about half of the inputs on this card. 

A larger image then the one above is available in the cabinet image archive.