The suspension of a 95 F350 is not really much more modern than that of a 59 F100. Just leaf springs and shocks. The big upgrade would be the axles from the F350. The spring mounts on the axles could always be cut off and new ones to match the location and spring size of the F100 frame welded on. You could have a spring shop build up a set of springs as heavy as you want and with as much arch as you want that would fit the frame mounted hangers. And you could rig up stabilizer bars for the front and rear, or just buy something from someone like Hellwig.
But keep in mind that the frame is your limiting factor. A 1 ton suspension under a half ton frame still results in a half ton truck.