So im going to be doing something similar in a 360 swap. I dont have a viable way to run a 243 as a manual shift without a ton of fab, a ton a swing joints and a ton of moving parts. So im going to use a electric shift motor. This is my plan for it. I can get a picture from the ford wiring diagram book tonight to show exactly what you need but all you have to do is plug in the ends and run the command wires for the relays to a two way switch. If you want to get fancy, you can splice some diodes in the return ground of the relays and a indicator light.
Simplest way for you would be to find yourself a 4x4 wiring harness from a super duty. Skip the entire computer control systems.