Butch D: In post 2, I was assuming you have a static loading. But now we see in post 4, you have a very different application than what I assumed in post 2. For your application, your square tube needs to be able to support a higher load than what is listed in post 2.
Therefore, if never more than one person is attached to your square tube, then it appears you would need to either decrease the length of your current horizontal square tube to 1090 mm long, or if you cannot shorten it, then it appears you would need to increase the horizontal square tube cross section size to, e.g., 57.15 x 57.15 x 6.35 mm.