NP205

The most popular transfer case to swap in is the NP205 by far. The 205 is an all gear case with a crunchy cast iron shell. It's very similar in look and construct to the Dana 20 with the exception of the 205's ~30% wider, helically-cut gears.

The thing is really a monster! There are however some drawbacks that keep everybody from doing it, the number one reason being the lack of a decent LOW gear ratio, but we will get to all of that later.

The question I have to ask is, so why wouldn't Jeep have been complementing their awesome line of trannies, solid quality motors, and beefy Dana axles with the tank-like NP205?

IMO, the underlying reason probably involved money. I'm reasoning that NP205s were not produced in nearly the numbers that the Dana 20s were. D20s came stock in IH, Chevy Pickups, Early Broncos, CJs, Wags, Cheros, etc. etc. In short, the 205s HAD to cost more right up front.

Then there was the issue of the added cost of an additional batch of parts that the NP205's mounts would require. It was no coincidence that the Quadra-Trac produced by Borg Warner solely for Jeep happened to fit the self-same mounting system used by the D20. Both Kaiser and AMC were producing the J Series from a cookbook of commonly available quality parts to keep costs down. They didn't have the luxuries of the Big Three's deep pockets, so I find it likely that tempting as the 205 may have been, it just proved too costly.

This is where Jeep's problem becomes yours if you want to

The NP205 is really the way to go if you are going to beat a Big Block truck with big tires. To install one is to really make a commitment to the whole thing because of the expense, mods required, and 2:1 LOW range.