Indeed, the rooster comb inside can vary, but I am not sure that this should come into play, given the years of the parts you used. IIRC, '68 was the last year of the single pin NSS and reverse lights from elsewhere.

It would be very useful diagnostic information if you could establish that the switch and comb are or are not truly the source of your problem. Doing so might avert the need to start digging into the internals of the transmission needlessly.

I would suggest that you disconnect the harness plug from the switch, and use an ohm meter to establish if the outer two pins in fact have continuity in reverse/drive/2/1 and no continuity in park and neutral (matching your symptoms).

a. If this is the case, it's bad news and time to dig further into the switch integrity and switch/comb interaction.

b. However, if the outer pins behave as they should (continuity in reverse, and no other gear), you can breathe a sigh of relief and continue your search external to the transmission itself.