Continue to troubleshoot or start from scratch?

Hi again, been crawling around the car for the last few nights tracing wires, cleaning terminals, etc. I unbundled the neutral safety switch harness from the headlight harness and fished it down to the transmission. Jacked up the car and crawled under. Having never hooked up a neutral safety switch before, I assume I'm looking at the right place, right below the shift lever. What I found there won't connect to the 3 prong plug I fished down from above. Any ideas what this is? It's a threaded stud with a nut on it.
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OK, I've discovered that is a single pole NSS after doing some Google sleuthing. My question now is, can I swap out that switch for the 3 pin switch and use the existing harness, or do I have to do some rewiring and just connect a single wire to the ignition relay?

That is the 60's style neutral safety switch... Someone put the old style NSS in instead of the newer 70's style...

Order the correct neutral safety switch for 70 or later... Since you're working on a 74 car, look up a NSS for a 74 Dart...

However, be ready for some trans fluid may leak out when you remove it if the trans is full...