I modified my HF QH, replacing the bolts holding the upper hooks with slide-in pins that have hairpin clips so they don't slide back out. It's easier to set the top hook higher or lower, or in one case upside down, to attach the implements.
When I went to mow real uneven ground, climbing the terraces between my orchard rows, I looped a chain around the top of the QH and top of the mower's hitch so the gap where the top hook should be, can open up to three inches. Then I shortened the tractor's toplink 3 inches. This lets the mower follow the ground contour better.
Here's a photo I posted previously. It shows that 3 inch gap closed temporarily due to the extreme angle between the tractor and the mower.
http://www.tractorbynet.com/forums/...ing-big-twin-ym240-vs-p1350118rym186dmow5.jpg
An upside-down top hook or the chain loop might work for you instead of modifying anything.