55.2-59 Wheelbase

[dsraven]

since the rear fenders also have that sloped or angled rear wheel opening, are you basing the box mounting based on how the tire looks in the fender opening or are you setting the box on the frame by going on the factory drawings? just wondering if the sloped rear fender opening is skewing the whole thing?
if you want to work from rear to front then I would say start with the box on the frame, levelled up, where the factory says it needs to be, then get the "front of cab" dimension (firewall) set by the same standard and get the cab levelled up there, then set the front sheet metal on and see how it looks. of course you should also mock up the front suspension first and have a wheel on the hub so you know it is how it will be. possibly the control arm is not quite centered on the cross member up front so the wheel may be forward or aft of the cross member centerline?