where is neutral safety switch

If you know where the 3 wires plug in at the transmission, you already know where the NSS is. That connector on the tran is both NSS and reverse lamp switch all in one switch.
From there you are nolonger seeking NSS. You are sseking a starter relay for the brown wire, and fused 12 volts for the white of purple with white and continuity to the reverse lamps on the solid purple.
I'm starting to think maybe you have the NSS wire harness that belonged with a 78 model car. That harness may infact have a odd connector on both ends. If it does have a connector at the firewall end, you'll need to cut it off and route the 3 wires in the earlier 70s model fashion as I have attempted so hard to detail..