Wiring up a neutral safety switch

Simple. You disconnect the clutch safety switch wire, and connect that relay terminal to the center pin on the transmission switch. The outer terminals on the NSS switch are reverse lamps

That relay is dead simple, here is what you have:

The huge stud is a junction point and one of the relay contacts. It connects to hot battery at all times

The large "square" screw is the other contact and goes down to the starter relay

That leaves the two push-on "flag" terminals. They don't matter. One goes to the yellow start wire from the key, and the remaining one gets grounded in park or neutral by the NSS. In a stick car, that terminal runs back through the bulkhead (separate grommet) to the clutch switch.