Well, I don't recognize anything there, except the "NP" could very well stand for New Process. I tried to identify a date code but the 2 set of numbers that start with C has one too many numbers on it. Maybe some one with some more knowledge than I have will jump in and help.

By the way, looks like I'm wrong on any possible older 5-Speed Overdrives.

I found this list over at Jolly's site:

http://www.6066gmcguy.org/SM420.htm

Scroll down to the listing of 5-Speed Transmissions and there is at least 4 that were available.

Bill

'60-'72 Chev/GMC Fan
GMC 9500 Fan
Detroit Diesel Fan