IIRC the 80's injected Chargers and maybe others used a speed sensor that connected to the trans and then the speedo cable connected to the sensor so you could have both. I don't know if they used the same counter though. But I think there are only 4 poles in the sensor. If you keep the speed sensor and brake light switch signals you won't have to use switches for the O/D and lockup.

I'm going to swap a complete 93 Ram Charger dash, engine, HVAC, fuel tank and wiring harnesses into my 74 crew cab. I plan to use everything from the RC including the steering column so mine should be easy. What I would like to do though is an OBD II swap for the engine management so I can modify the engine with an intake, cam and heads. The hot wire harness looks like an easy way to go but at $1000 it's pretty steep. Especially when you consider you still have to get a PCM and tune it as well. So it may remain stock for awhile.