You can probably find a Nissan factory service manual for your 720 at Nico Club's site, which would have the wiring and vacuum diagrams for the different engines. If you have both trucks, the best thing to do would be to swap the harnesses and ECM. Yeah, it's a pain, especially when dealing with 35-year-old wiring and brittle, plastic, connectors, but it takes a lot of headache out of figuring out which wires you need and don't need.