Need assist with transmission identification and driven gear removal

[HIGHWAY BY THE SEA]

The speedometer in my 67 3500 has not worked in at least 20 years (title confirms). I checked both the original one and newer replacement by spinning the cable with my fingers, and they both work. But neither works with the speedometer cable hooked to the transmission. The cable will not turn at all (tested it by driving the truck with my finger on the cable tip). So I tried to take the driven gear out of the transmission, but could not quite figure out how. Below are pictures of the transmission and driven gear attachment. What kind of transmission is this? (I think that it is a three speed on the floor with an "L" gear listed on the shifter knob). And how do I remove the driven gear?