My thoughts on adding the transfer case was to provide a creeper gear. That probably isn't possible with a standard transmission, and if it is, then a rebuild is needed to install the creeper gear and you then loose one gear, because it would be so low that it would not be used, or useful, in every day driving.
With the VW, the transmission change, as you suggested does work. The 4wd (Syncro in VW terms) transmission (actually a transaxle) adds a 5th gear with the creeper gear So it is basically a 4-speed plus creeper-granny gear. I don't think such would exist for American iron, but I am not super familiar with such. VW does not use a transfer case, hence the addition of the creeper-granny gear to the trans.