408GT; An I beam is a structual piece used to carry heavy loads throughout its length. They do not bend or flex very much up, down, or side to side so they make good building supports, but are not designed for what you are using it for. I imagine there is a good amount of mud where you plan on wheelin. The suction alone from a good mud puddle can triple the weight of your truck and that I-beam does not even look to be more than 1/4" thick. I bet the first good straight pull on that I-beam will rip it out at the thin spot. At least box it in with some thicker stock to the front and sides so it spreads the pressure out. It would not be too much more work, and would make it real strong. I am just going on about this because I worry about people getting hurt or killed when stuff comes apart.
Nice clean welds by the way.