my 90 cummins has 99-05 f450/550 leafs up front with a chevy d60 under it, cross over steering and a track bar. rear has 63" chevy leafs and a 14b out back, bilstein shocks all around and it rides great down rough dirt roads, the nv4500 sucks towing heavy loads in the mountains. i have a nv5600 laying around i need to swap in some day. if i was doing it over building in stages like i did only thing i would change is switch the chevy 63" leafs for some newer ford 08+ 66" leafs. if i was starting from scratch and purchasing it at once i would go with 05+ ford axles and the suspension with a nv5600/g56 and 271 driver drop t-case.