Is it possible the leaf springs were seized up from sitting ? The examples I have seen on auction typically had only 30k miles after 50 years of service ?? My 1968 series 2 land rover suffered from that mallady until I did a few hundred miles of washboard logging road, after that it was like a new vehicle ! (I did have to grease the leaves after that to stop the rust forming again). If the suspension stays too hard, one could start removing leaves until one liked it and add air bags for load. There have been substantial strides made in suspension design in the last 15 years, let alone 50..
I don't think I am too worried about the speed. I don't think one can compete with conventional freighters who will bid on moving whatever it is you have via sites like Uship.com. I am concerned about dealing with bad roads and have no idea "effectively" how a conventional semi tractor can deal with severe washouts and how the suspension articulation works on them. Also don't know if anyone actually makes lockers for semis for low traction situations. I'm sure some of the semis will have low enough gearing, but then one has to be sure ground clearance issues are addressed too.
What puts me off the dump trucks is that they are typically so high and the dump bodies are really heavy. My loader would never reach high enough to load a normal height dump truck. So for hauling sand and gravel, I will use a dump trailer exclusively, but these are heavy beasts loaded, and I'm not sure an F250/350 is going to be up to the job. Maybe if they actually have a 3/4 ton over the rear axle they would have some traction, but it could get interesting on the downward slopes... My limited experience is that one wants the biggest rolling diameter possible, and that usually goes along with big brakes...
I'm trying to think through the things that would be dealbreakers. If for example one could not get reasonably priced axle replacement parts, or if the supply of Mil surplus tires dried up, those would be very expensive consumeables. The transmission, if prone to breakage and expensive to fix could be an issue.
Power steering could be retrofitted, there are very much standardized systems out there today. Basically, it seems to be a fairly simple truck, not at all refined of course. It fits under the CDL requirement and could do so when towing a trailer, provided that the truck itself is not loaded too much. Besides which, on the roads I may need it on, I doubt anyone will be checking drivers licenses too frequently, let alone consider that the nearest truck scale is probably 70 miles away on I25.
It was the roughest riding vehicle I ever drove over the road. Another problem was it would only do about 50 MPH.