Trans and Transfer case & exhaust manifold?

[SunSoaked]

First off- thanks in advance for the collective knowledge made available on the site

I bought a 69 C10 4x4.
I intend to swap the factory 4 spd with a 700r4. I also believe the transfer case is a np205 based on the fact I can stick a magnet to it (assumption=cast iron).

Questions:
1. Will the 700 bolt in, in place of the stock 4 spd? What mods (x member) are required?
2. Truck has over 100K miles. Should I need to "overhaul" the transfer case. It works fine and doesnt leak. If it's gear driven, are there any parts inside that "wear-out"?
3. I have "ram horn" style exhaust manifolds on the stock 350. My neighbor told me those were desirable and people were always trying to find them. It appears they were used because they rise up and allow more room next to the block for the clutch linkage and crossbar. I was thinking on using traditional headers with the swap to the auto trans. Are these manifolds really worth using?

Thanks, Mike