From what I've seen, there are two computers, throttle bodies from the M104 with each running one bank as the M120 is just two M104 engines put together. I'm not sure if the two talk to each other.

The 4 speed trans will be hydraulic shift so the only info will be output shaft speed ( speedo ) , there might be a input for gear selector position ( neutral , drive ) . The 97 up electronic shift 5 speed talks to the engine computers.

Someone ( in England I think ) was building a kit car / Lotus 7 type with the M120.