I'm not aware of a box that specifically fits your enclosed driveline, but I have seen literature describing boxes that could be paired to enclosed drivelines, of course they required changes to the driveline enclosure. Finding one for your application will not be easy even if one existed 75 years ago.
I have a 5831C in my truck, all 3 ratios are road usable and split the 4 speed both up and down in every gear sequentially. See videos below for an example of how it drives. Overdrive is 0.85 so you can add about 17% to your top speed on level ground. As always, the rest of the truck especially brakes will need to be in great shape if you are going faster.
