I have one in my 69 C50 and it works rwal good in the mountains and hiways, but in your case you may be better off playing with tire sizes and rear end gearing, because of the mechanical effeiciency of the unit, the fuel used driving the extra transmission you will most likely get the same fuel mileage.
I already have the largest tires I can run with the flat bed.
Gears are about 5:38, thread I have read here indicate that changing them is difficult and expensive.
A Gear Vendors unit would be nice, but VERY expensive.
