4WD would be G58 transmission and chaindriven/planetary gear t-case. The G58 is not compatible with non-SR5 gear-driven t-cases.
You can either find another G58 from an 86+ 4WD truck or get a W56 and gear-driven t-case from a non-SR5 22RE truck.
I would suggest the latter as it's upgradeable to dual cases, crawler gears, etc, whereas the G58 is not. It's a bolt-in swap, no mods necessary.
Hef