Having just done this by myself, it can be a chore. I took out my 700R4/NP208 combo separately and it was rather easy. Just get a nice piece of plywood or a 2x8 to spread the load across the pan and lower away. Then I put a TH400/NP205 combo in it's place and found it a lesson in wobbly futility. I put a 2x6 lengthwise spanning the front of the tranny pan to the crossmember (still bolted to the t-case) because the front-back balance point seemed to be about 3" in front of the crossmember. I also found the t-case doesn't balance too well left-right and the whole assembly kept wanting to tip off the jack. It's certainly helpful to have a second set of hands and a jack with a bigger saddle (the one on my craftsman jack is only 3-4" across).
Good luck and don't hurt yourself.
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