I put one of those kits on a 1950 about 10 years ago and it is the last one I would ever do.
If you mount the box at the angle they recommend, the drag link end, the one that attaches to the steering arm, was at such an angle that I feared it would snap if the truck was put in any angled position where the axle would drop or raise on one side.
I mounted the box on this truck much more level than the instructions and that made it better, but not much. This truck also ended up with much to sensitive steering. I had to mess with pump relief valve to lower the pressure. What a pain.
I would never use this kit again on any customers truck simply for the liability issue of this bad design.
