Steering Linkage Interference

[65 C20]

I just added P/S to my truck a couple of months ago.
I used a Moog K6131 pitman arm with no trouble.
I have a 65 C20 and the sway bar mounts differently than yours.
Like you I don't know all the names of the front end parts, but where the sway bar connects to the lower A arm (I will call it) it has the same type of rubber bushing and clamp as where the sway bar connects to the frame rails. It sits lower than your connection.
As far as how far the pitman arm goes on the steering box shaft I have approx. 5/8" space. The nut that I used was the same nut as the manual box and it was quite a bit thinner than yours.
I am not sure if sway bars are different for 1/2 ton and 3/4 ton or not.
What pitman arm do you have?
Cal.