Ouch, that hurt.

Well, it has been cleaned up significantly since those pictures were taken. All those wires hanging down are the original MK2 buttons/joysticks which were just removed from the CP and dumped into the cab. That's been fixed, they are now correctly connected to the corresponding buttons/joysticks on the CP.
Same with the second pic showing a mass of wires under the CP connected to the encoder. Got rid of the encoder and things are much, much cleaner now.
It might not look like much, but I took great pride in converting the cab. I'm not used to working with my hands or dealing with electronics, so the fact that I have set up a fully functional MAME cabinet is a big deal for me.