Nice idea. What thickness is the metal? In any case, I'd weld some triangular gussets in between the horizontal and vertical faces of the metal, on either of the hitch ball, to discourage twisting/sagging of the horizontal part of the angle.
Grade 8 and 1/2" bolts. Like I said I only am pulling a light weight boat and I hauled a trailer for over 300 miles last weekend and worked great. There is 9 half inch bolts holding the angle to the Jeep. I am getting it welded together this week anyway.