A gearbox I made this morning. There is a 11:60 gear reduction from the CIMs to the shifter shaft (this can be increased to a 12:60 reduction). From there, it can either undergo a 1:1 reduction to some 32t #25 sprockets or a 3:1 reduction via a planetary gearset to the same.
It utilizes a 1 Module (~25 pitch) 60 tooth internal gear to make an epicyclic gear set with a 30 tooth sun gear. It can shift between a gear ratio of 5.45:1 in high gear or 16.36:1 in low gear. For a 5" wheel, that means 21.2fps and 7.1fps free speed; a fast combo for a large field.
Using a 12t pinion, you can get 18.5fps and 6.2fps from a 4" wheel, a solid set of speeds for a 6-cim drive.
A .stp (STEP) file is available here:
A shifter piston has yet to be added, but you can put it either in the front of the gearbox or in the back.
This is not WCD compatible, as the output is via the two 32t sprockets only.