Rotating the posts looks like it would change the angle on the arms, wich would affect the angle of the rear vertical posts, which would be bad, as that would limit how far down the loader could go, and it doesn't go far enough as it is.
I think the best solution is to get the gaps as tight as possible, and weld the hook plates to the horizontal arms.
along these lines, I have batted around the idea of welding on some guides that would keep the front mount from moving side to side, which on my tractor, they do about 1/2" each direction.