As awkward as it is I would bolt the tranny and transfer case together before you put them under the rig. I think it would be alot easier in the longrun than trying to get the 6 bolts to line up while your upside down and a couple of them are real hard to get to if the crossmember is in. If it's not in then you have to support the tranny while you lift the transfer case.
Jim W.
I disagree here - install the transmission alone, its going to be fun enough...
After you get the transmission bolted to the engine use a jack on the intermediate housing to hold it up (I've seriously used a ratchet strap over the top of the frame rails to hold the transmission up too - you can do it by hand, you just dont want the fan into the radiator or shroud up front)
Now you can toss on the transfer case - I've done D20's, NP205's and the Atlas II, you can get to all of the bolts easy enough. Once you get it bolted on, lift it up and put the cross member into place - easy stuff with a jack.
Take a look at my build thread, I go over all sorts of good info and picture everything of interest in my NP435 install. Link is in my sig-
2WD NP435/Kurt's 1" adapter/I-6 Intermediate/D20