Bill,
I would try to get an OBDI harness. It will make tuning much easier. THe wiring of the LT1 PSm is actually quite simple (although it dies look daunting!)
You actually only end up having to connect these wires:
4 injector power wires (12V ignition +)
1 PCM pwer wire (12V constant +)
Fan Control (the PCM earths the relay)
Fuel pump control
Everything else just plugs from the PCM to the engine sensors via the OEM LT1 harness.
Then the gauge input wires:
1. Oil Pressure (I used a mechanical gauge)
2. Water Temp
3. Oil Temp (I used the oil level sender hole in the oil pan. This was just a nice extra gauge and is unecessary)
4. Volt meter.
5. Tach.
6. Speedo.
I used all Aftermarket gauges (Autometer Ultralites). I actually have NONE of the original electronics in the car. I am using the Honda S2000 ingnition switch, toggle switches for lights etc, no heater, defroster, or windshield wipers. I think the only original Datsun part remaining are the tail lights.
Let me know if you need any help when you get to the wiring.
Tim
Tim