i've been getting quite an education about this. after talking to fabtek and kelderman, you should be ok, what i was told was that the dually and excursion use a 4" tube, and the f350 srw and f250's use a 3.5 tube on the front diff. i wanted to put the fabtek coilover kit on mine, but was told i'd need to do alot of grinding to make it fit (99 f350 drw 4x4).
the other coice for aftermarket coilovers is skyjacker, i was not as impressed with their z-link kit.
keldermans kits are absolutely massive, i have the airride rear kit, with the 8" lift.