64-66 Sub 4 X 4 drivetrain updating question

[earl84]

I am not in the market yet for one, but I would love to get a 64-66 4 X 4 Sub and put a more modern drivetrain in it. I have pretty much finished a 66 C20 minus paint, and had a lot of fun with it. Just trying to do a little research on this before I start looking to buy, probably in a year or so. Not very easy to find one available for purchase, for sure.
I want to do a complete body off restomod, install an LS engine, 4L80E trans and transfer case. The transfer case is where I start getting out of my comfort zone, in terms of how does it mount to the frame, is it fairly easy to modify a newer one to fit underneath, etc. I can't seem to find this information after searching for quite a while. Maybe I am search challenged, haha.
I know it will all be a big job, but my C20 was a big job, and I learned a ton with it, turned it into a decent daily driver, and feel pretty confident with everything else.