maybe you may want to try this,,, get a square receiver tube, drill a hole in it insert a headless bolt ,,weld it,, now you can install it on top of the bar where you were going to put the ball or you could put it under the bar where the ball goes,,, you can drill two small holes one on each side, just put bolt therogh bar and tigjten nut to make it ridgid, so it does not swivel,,
jim