The dual transfer cases I've seen, are usually an aftermarket product, and usually kept quite short to help keep the drive-shaft angles from getting too steep. Not usually "Hi-Low", usually straight through and Low.
Done right you crawl real slow. Done wrong, you break things. ...a lot.
I've got dual air lockers, and switched to a larger engine with 2.5x torque, and a trans which has a lower 1st, with the attached t-case having a lower low range than the original.
Looked at dual, but just didn't need the extra crawl torque, since I can already stand it up a wall to the tire traction limits.
I had the slip-yoke eliminator added, which helps keep the drive shaft longer, and then did a center spline rear drive shaft with Spicer over-size c.v.'s.
All drive angles are still less than 2 degrees.
I learned to weld to get what I wanted...
...Rubicon survivor!
/4x4 geek