No mandatory seat-belts till 1966! They were an option to keep people from bouncing out on bumpy roads, not for accidents. They were first patented in 1955. Just my 2¢
Polara, Pioneer & Seneca all used the same front sheetmetal, just different trim and Polara had its own grill. Dodge was making Police cars in 61, here are some promo lit!
"Good", the neutral switch is working correctly. The wire from your NS is probably brown it should be plugged into your starter relay. If it is, pull the brown wire off and ground that tab from the relay to any ground. Now with caution making sure your car is in park because it will start in...
Call Clay Kossuth 636-257-4669 he is in Missouri and will probably be able to help for less $$. He is a very good source for old MoPar parts.
Tell him Herb sent you.
How did you test it? The center lead is the ground for the starter relay. It should only ground in N & P. The two outer leads are the back-up light leads that complete the circuit in R only. To test the neutral switch you need to have your test light attached to a hot lead such as the + on...
http://www.imperialservices.net/Imperial%20Services%20-%20C-Body%20Parts.htm
FYI
Steve makes A, B, & C body mounts. He also rebuilds your push button shifter to operate a newer transmission. Tell him Herb sent ya!