To bring it back to the OP,
I have made a 4 link of my own that I run on my 06 f350 with air bags, similar to the Icon, probably a little heavier though. 2" x 1/4" wall is plenty of tubing for anything that truck will handle. Its a heavier bar then you think.
For the bracket , 1/4" is fine, remember the frame of the truck itself is 1/4" so as long as it is made smart then it is good. I would tie the bracket into the side of the frame and not just bolt to the bottom.
On my kit I used 5/16 plate and have had no issue at all. Very strong, remember only one of the bars is relying on that bracket the other uses the factory bracket!
A couple pics I had not great ones.