The 6R80 is still a distant dream for most, not that many actually in Broncos. I would guess less then 100 in the wild. Now asking about mating a 12 year old aftermarket transfer case to it? Pretty good odds that you are the first to even try this.
Do a bunch of measuring and test fitting, where are the limitations? If the transmission output shaft is shortened, how does this affect the transfer case input shaft and will it now bottom in the transmission case?
They do make spacer rings if you have to shim the transfer case back so it doesn't bottom inside the transmission case.