1966 4sp vs 1975 ? sp differences.

[vince1]

I saw a transmission in a 75 P/U with the gear shift stick missing so couldn't tell the number of gears or shift pattern. Looking underneath it looked to me that the transmission, as well as the bell housing might be different. It was cast iron case with the PTO plates, one on each side. Any chance they had 5 sp back then, or what would any other differences be to the original one that came as OE in the 66? Thanks.