[Root2812]

You may be mistaken on either what you have or the story. The 1/2 ton didn't come with a 235, it came with a 216. The big trucks and busses came with a 235 but it was a splash oil system like the 216. Don't mistake that with the 235's guys swap in because those are the 1957+ with full pressure oil system. So either you have a non-original motor or you have a 216.

The 1/2 ton came standard with a 3 speed on the column but the 4 of the floor was an option. Infact my 1/2 ton has the 216 with the original 4 on the floor. Its most likely a SM420 if its original and could be either that or maybe a Saginaw if its been swapped. Do you have the remains of a column shift on your steering column? If not then I would bet you have the original sm420.

My truck will go 50 mph but the motor is screaming. That has a lot to do with the factory 4:10 gears in the torque tube rear end and not so much the tranny. The sm420 has a very low 1st gear to where you don't even need to use it unless you are pulling out stumps but the 4th gear is very similar to the 3rd gear in the 3 speeds. These trucks were ment for farms and not highways. If you want highway speed your best bet would be to find a 1957+ 235, a t5 5 speed (s10's had them), and an open drive rear end. All those parts are cheap and would give you a more streetable set up.