The reason I looked at this thread, was because my neighbor just got a tractor, in order to mow with his wife's uncle's 6' Woods brush hog. In the process of mowing, he managed to rip an interlock wire off, which i repaired for him.
In any case, he mentioned that he had bent the steel A frame on the B/H, as well as sheared the bolts off more than once. Being unfamiliar with the "swinging top-link" mechanism, at first glance, I suggested the chains, rather than the steel. In retrospect, I see now, how the swinging top-link works and I believe, his top-link was too short for the tractor/Brush hog set-up. Having only glanced at everything, I believe, he had the top-link well stretched out, probably to reach the swinging top-link assembly, and even then, every component was in alignment, rather than flexible. This configuration, would make the whole action of the swinging top-link similar to a rigid assembly. ... in other words, there was "no swing" available.
I'll have another look, and if applicable, suggest a longer top-link.