i have a 1999 f350 crew cab dually v10 its 2wd i was wanting to covert it to 4wd (if its posible) has any one done this and if so what will i need and how hard and expensive is this

 

Its possible, but not very cost effective. You'll need a new transmission, transfercase, front axle, and suspension. The 2wd uses an SLA type coil sprung suspension where the 4x4 uses a solid monobeam leaf sprung axle. You'd have to get a whole parts donor truck to work. You would be money ahead to trade trucks. Parts alone will run you over 5k, let alone the labor and down time for the truck.