I can’t help you with the assembly portion of your question, but since the broken piece is missing, I think you would be better off, cutting the rest of the circle/arc off (in an arc along the o.d.) and welding a new piece of cut tubing with the same length, o.d, and a slightly smaller i.d. and ream it. It would probably be easier than trying to fix the break. Just make sure you you get it in the same spot... take dimensions and trace it out on paper, before you cut it off.
And like Todd said, get a good welder to do it.
Just my two cents,
Last edited by Speedracer; Tue Jun 12 2018 11:23 PM.