I beleive the stock th400 4x4 is the short shaft, the long is on the two wheel drive where there is a slip yoke.
My advise would be to not buy the adapter and go ahead and get your 205/203 built with shifters you want to use and have it sitting there waiting on the axles. The 203 takes the place of the adapter.
Keep driving the truck with the 208 until all of the parts are collected. change out everything at once and save money on doing things twice. otherwise you will be modifiying your driveshafts several times.
If I were doing it again, I would not pull anything off of the truck until my lift, steering, trans and transfer case parts were received to do it all at one time.