Transmission identification a833

Trying to learn more about my 4-speed. I have Passon's book but im still not finding too much. The tail shaft is stamped "C39126-3" or "C99126-3". The book says the 99126 was used from 69 to 71. The car its in is a 67 barracuda and the car it is believed to come out of is a 72 duster. What does the -3 mean? The VIN on the case is not readable but it is stamped "C99129-L" on the main case not the side cover. The book doesn't say anything about that. 20200501_112546.jpg 20200501_112550.jpg