First off the transfer case would go right there your passenger seat is, and mean RIGHT WHERE it is. I don't believe there would be room for the seat if you were to put the transfer case there.
I am thinking a 700R4 will do the same thing as you want with a lot less hassle.
One rule in my mind when making mods on a car, a house, whatever, don't do them JUST BECAUSE you have the stuff sitting there doing nothing. Build what makes sense.
Look at it this way, ask yourself this question before a modification like that. "Would I do this if I didn't have that transfer case?" If you only had that motor sitting there in your garage and were putting it in your Olds, would you go shopping for a transfer case and cut up your floor to put it in? If that IS something you would go out of your way to do, then do it. But don't do it just because you have that transfer case sitting there.