[blucar]

If you want to improve your gearing find a two-speed rear end for it.. I have a '36 1-1/2 ton flat bed that has the two-speed option.. A two-speed rear end gives you the best of two worlds, low gearing for power and high speed for highway speeds.
The two-speed differentials of the '30's were manual shift, no vacuum/electric. My '36 FB has a shift lever mounted adjacent to the left, next to the cowl. The brakes on my truck are hydraulic, which looks like a factory application, however, I have been told that the '36 trucks had mechanicals like the cars.. My truck also has an air brake system, however, it is not air over hydraulic, it appears to have been for towing.
I was raised in a farming area of Eastern Idaho. During 1951-52 I worked in a farm shop that did all kinds of things to modify the '30-40 model trucks to have more power/speed out of the small engines. Aux transmissions, usually out of another truck being placed frontwards and/or backwards depending on if the need was for more power or speed.