I mix with last cabinet with pivot guns I fixed, was a Alien 3, sorry. Same kind of gun but with a button for grenade. I know motor and chassis are the same, since I think I've use a motor and internal rumbling system from a LA MG or GB NY to repair one Alien 2 gun. Long time ago.
Ground wires go to metal parts of the gun (chassis). No really needed, just security, as you have ground wires to metal doors or panels in cabinets.
The gun is easy to open. First take off the handle, and after a few screws and you can take off half of plastic of the gun.
ANd if you unscrew the...
If I remeber well, playing it long time ago in Japan, Special version use uzis guns instead of pivot guns and 2 opposite screens with a charriot that turn back 180° one to the other. The 2 screens are just alive one at the time.
The microphone adapter is the same that come with Planet Ring, except you have a wire to the mic and not directly plugged in it. The PCB part is I think the same than in a DC controller (but not full, like in arcade sticks or others).