The only ones I know about fit 4x4 transfer cases. If it can be mounted behind a standard rear wheel drive trans you should be able to use it as you describe -- high rear axle then run in "underdrive" unless on the highway. I'm not real sure those things are made to run long distances at highway speeds though. Most are only used off-road, which means lower speeds for a shorter time. Try going to the Novak website. They deal a lot with Jeeps and other 4x4s, and may have some info on that particular unit. Also try Advance Adapters, I think they sell an underdrive unit.