Having done a 4x4 swap myself, I completely agree with Scott that a whole donor truck is the way to go. If you can find an early bullnose one that has the wiring you need then so much the better, you kill two birds with one stone. Just remember the 4x4 parts are compatible through 1996 which opens up a lot more options when looking.
SHORT BED 4-DOOR DIESEL: 1986 F350 4x4 under construction-- 7.3 IDIT ZF5+GVOD
STRAIGHT SIX 4X4: 1981 F150 2wd to 4x4-- 300 I6 close ratio diesel T19, hydroboost brakes, Saginaw steering
BIG F: 1995 F-Superduty under construction— converting to 6.9L IDI diesel ZF5+DNE2