Welcome Aboard;
As for safety posts. We had two for our 1970's PU, that we purchased. We installed them in opposite corners. Ours were made from some light weight steel. Looked like formed sheet metal in a U-shape. About a foot from one end, there was a welded on "Z" bracket. You could use it as a lift point in the palm of your hand if a cable broke, you could use it to help lift the roof, or lower it. We did have cables break on that old PU. I think each end had a could notches in it too.
When I did a quick google search. I saw a partial image of one made from ABS pipe. I also saw a video of a metal one something like what we had, but no Z'd bracket.