I'm new to posting on this board, and I'm not sure I understand everything that's going on, so I may or may not be helpful.... however.... :-)
I'm working on adding two Williams 49-way optical joysticks to a MAME setup. To do so you would want an encoder (like a GP-Wiz49 MAX 49-Way Joystick USB Interface), and a cable harness for each joystick. I was able to email Randy and Bob and purchase a solution. I don't know if they were doing me favors or selling me products, but I'd be happy to explain what I did and see if it can help you. Dunno if you can PM or email me, or just give me an address to email you...