Is the speedometer cable connection different on the '79? I know they changed at some point (threaded on earlier?) but that would be about the only issue I can imagine. Well, and getting fused ignition power to the VSS buffer (the box) but pretty obvious issue there. 
You are correct on the t-cases. Eliminating the cable and being able to change the speedometer for gears/tires pretty simply is great, but the cost of a t-case swap adds up quick.

You are correct on the t-cases. Eliminating the cable and being able to change the speedometer for gears/tires pretty simply is great, but the cost of a t-case swap adds up quick.



