what would it take to convert a 2wd truck to a 4wd?

 

a lot of $$$$ and time!

 

Transfer case
Transmission to Transfer case adapter(tailhousing) and tail shaft
Front driveshaft
Rear driveshaft
suspension
Oil pan
Front axle
Steering linkages
engine crossmember
shifter linkages for transfercase
Transmission crossmember
brake lines

I'm sure theres more, I can't think right now though.