Welcome to the forum
Fourdy!
Beautiful Camper you have there and would love to see more photos.
The PS Bracket was made two styles, that I am aware of, from the factory.
Some have used other style of brackets that were fabricated or borrowed from other applications and "made to work." (Last photo)
The key is to procure the factory double-groove water pump and crank pulleys and that can be a challenge. They came on the light duty and big trucks too.
You may wish to post a WTB in the for-sale section or PM RUSTBUCKET as he sells parts.
Photos of the two styles of pumps; the big round version (Left) is early and the thin one (Right)
These pulleys are the most common version I have seen, but some were also cast iron. There was even an add-on pulley for the crank, but I think that was for AC applications, but could be made to work.
The last photo is a fabricated system I think made by Member RockDriller.
Hope this helps and here's a CL ad that list parts for the GMC V6
https://portland.craigslist.org/clc/...456670840.html
**These are old stock photos I have saved over the years.