To swap over to a 700R4 from a TH400 you'll need:
a dipstick
a flexplate
torque converter bolts
a torque converter
a transmission
a 27 spline NP208 transfer case
a tall 700/208 adapter (they can be hard to find)
TV cable bracket (also hard to find)
lockup wiring
The two trans/t-case combos are almost exactly the same length, so no driveshaft mods are needed. Also, you go from a 2.48 first gear in the 400 to a 3.06 first gear in the 700 plus the 30% overdrive gear with a locking torque converter for maximum efficiency.
Also, the carrier break on a D60/14 bolt is 4.10 and down. You can run 4.11 gears on a 4.56 carrier. At least I'm pretty sure anyway.