I can't access wiring diagrams back that far, but Nissan/Datsun ignition switches pretty much all have the same 4 or 5 wires, so some of it can be deduced from the present hookup. One will be battery supply in, that will be your WHT/BLK. The "Start" terminal output looks to be BLK/RED, that will be the trigger wire for the starter solenoid. The remaining wires will be Accessory and Ignition, and it looks like he wired them both to the Ignition terminal. To figure out which is which, jumper them individually to WHT/BLK and see what goes hot. The Accessory wire should power the radio, the Ignition wire should power the stuff in the engine box.