I bought a 94 ranger x cab, 2wd 3.0 auto with a wrecked front clip. Going to make it 4x4. You will need to change the engine crossmember as 2wd and 4wd x members are different. For what needs to be done, swapping the frame is less work, which is what I'm doing. My swap needs a new frame regardless as the original frame is bent too bad. In my area 2wd frames are the same price as a 4wd frame, so thats my justification.
Swapping in a ttb axle will require an engine crossmember swap, or frame swap. Either wsy you need yo pull the engine and unbolt the cab from the frame as the framerails need to be widened to get the old x member out and the new one in. If you SAS, then your 2wd frame can be used, and is actually easier than SASing a 4wd frame...
SVT