Grigg, from where I stand here in Kansas, the wheat state, there isn't anything about your post that makes sense.. you do know your stuff, however there is some disconnect here..
1) There are no short bed large trucks here. The farmers needed these trucks to carry every square inch they needed to haul as much wheat as possible. This means that we are dealing with long wheel base here.. between 25 and 32 foot trucks (total length). Maybe longer since the dealer had the beds made after delivery.
2) The beds were a full 12 inches wider than the widest part of the dually. They stuck out a lot wider than the cab. Since they all have dump beds (a feature I intend to keep and accentuate) they are much much longer than a normal suburban garage).
3) The gear ratio is secondary, but agree that its an issue but may or may not be important to the consumer. Just the same issue as when you purchase a 1/2 ton that's original and you realize its max speed is 50.
This puts these large trucks on par with the smaller ones. By modding them, cutting these long wheel base farm trucks down to a short wheel base farm truck, then making the bed a reasonable size, we are almost there. The next issue and one that will make or break the mod is reducing the number of wheels to 4 and making them modern radials. The standard axle I am thinking is too wide to do that without modification?
You are the one with all the knowledge Grigg, make no mistake, its just that I have ONE short bed ton and a half and its probably the only one in Kansas. The other 4 are outside because my commercial 10 foot wide by 30 foot garages are too small. I am with you on the rear axle not being the right ratio, but I am trying to start by making this cheap and on par with original half tons. Let the customer decide what to do with rodding it out.