Which truck / camp rig is taller (to the top of the camper including roof top equipment) and hauling the same camper: 1. F450 Cab and Chassis with a flat bed, or 2. F450 with pickup style box?
Fleet Ford specs shows F450 pickup shows 38.3" ground to open tailgate with a small 9900 rawr.
Same specs shows the F450 cab/chassis 34.8" ground to top of the frame rails with a much larger 13660 rawr. Specs does say these dimension may vary a bit with options
You will have to look at each upfitters bed assy to figure any differences.