Two structural beams I have to be brutally...stiff

[totem]

or honest.

I have no clue what I'm doing but this is the scenario:

I have to buy a 4.2 meters long steel tube. Two structural beams will hold it in place so yours truly can dangle monkey style on an aerial hoop.
My weight (+hoop) will be equally shared by 2 chains placed at about 2m and 3.5m (due to lack of space on one side).

Anyone can give advice regarding type of steel best suited for such a job and what specs I should be looking for since static weight will be about 55Kg and dynamic weight (I suppose) may impact the steel eventually?

Any help would be much appreciated!!!

[dalecyr]

What is this for?
And, a quick sketch of what you are thinking would be helpful...