First off yes, you can make it work..........Drop an LSX motor and tranny in. LOL J/K You'll need to purchased a 40-tooth reluctor ring for a 1991 NP205 and mount it on the output shaft of the transfer case. Then you'll need to either weld in the old speedometer hole in the case or make a bushing that can be shrunk into the hole with the threads machined or tapped in it for the new VSS. The housing is cast iron so you better be a good welder and preheat the case prior to welding. You'll need to make sure the new VSS is oriented exactly perpendicular to the output shaft and reluctor ring to get a good signal.