Does your truck have the "Walking Beam" suspension and the Power Divider? I missed reading about this truck being a Tamdem Axle.
It might be easier to find a single axle truck with a 2-speed rear and move your good parts over. You could build a running rolling chassis before you ever start swapping parts.
I've got a '57 6500 with a 2-speed rear (bad sheet metal, but a good chassis).
Send pictures...
Mike
