I had a 700r4 put in my 1972 K5 (NP205), and I love it. Assuming you already have a 350/205 combo you only need a few things.
1. A custom output shaft for the 700r4 that will mate to the NP205, available from Advance Adapters for about $175.
2. You have to move your crossmember back either 1-3/4" or 1-7/8 (I can't remember). The 700r4 is longer that the T350.
3. You'll need to shorten the rear and lengthen the front driveshafts.
4. Since the T-case is farther back, the shifter won't work in the stock floor cut out. In order not to do and sheet metal cutting & patching I just torched the shifter and bent it to work in the stock cut out. It just doesn't stick out of the floor as much as it did, but still looks good.
A few other things are you'll have a TV cable instead of a kickdown cable, you cooler lines will probably still reach, The computer thing is no issue, and if you wan't the lock up to work you'll need to install an aftermarket manual switch from someone such as B&M (about $200)(I didn't bother with one).
Last but not least I'd recommend adding an auxilary tranny cooler (especially with no lock up). I did and my rig now runs as cool as a cucumber.
Good Luck.
