As you can see in the picture below the shift lever is very weird. What could be the reason for this? Maybe it used 2 tranmissions back to back and this shifter layout allowed to operate both transmissions together at the same time in a compounded fashion without having to use a splitter in semi trucks?
The shift pattern is a double-H, just like it's shown on the knob. In neutral the shifter spring-centers, and could then be moved through a gate to the neutral of the other H. This shifted a two-speed hi/low gearset that was between the clutch and the main 3-fwd/1-reverse transmission.
The gears were not arranged in any particular way, they were just numbered in order based on whatever the ratios worked out to be. This type of machine is almost never shifted on-the-move. You just picked the gear you wanted to be in and started out from a standstill. Even high gear, which probably had a top speed of 17 or 18 mph.
CBT built ag tractors using Oliver tractor patents licensed from White Farm Equipment. This machine looks a lot like an Oliver 1750 or 1850.
This machine has 4x2 2WD wheel drive system, 6 forward and 2 reverse transmission system.
So it would appear that the operator uses one set of 4 gears or the other. Gears 1-2-R1 for heavyweight work with 5 for cruising, and gears 3-4-R2 for lightweight work with 6 for cruising.
I can't find any reference to the gearbox construction, so I can't answer whether there are two drive trains, or an overall ratio control.