Dumb question 3 or 4 Speed Muncie

[Legolas894]

Ok, in my GMC 910 (which is like a C10), I have a mystery motor that I think is a 283 V8. According to the VIN, it should have had a I-6. It also had a column shift replaced with a floor shift. Anyway, I put a new speedometer cable and red 21 tooth driven gear on tonight to get the speedometer to work (and it does yay!). While under the truck in the rain, I could actually see the casting numbers on the transmission. It was 3857584GM and another number is 3851325. A quick websearch says that this is a 4 speed transmission? I can only find three forward gears while driving and reverse is ok. The floor shift pattern is also a little strange Reverse all the way left and forward, 1st straight down but a little to the right, second over left and straight up and third straight down.

Does this sound right or is there a missing gear somewhere??

I feel stupid asking!!