On my JD the top link has little levers sticking out to turn it. I often get the jamb nut where I want it and then use the levers on the top link to tighten it up to the jamb nut. It seems to hold.
I give a small tug with a wrench on the jam nut. My problem is when removing the implement I sometimes forget to loosen the jam nut BEFORE I pull the pin at the implement connection. If I do that I have problem loosening the jam nut when I mount the next implement. Just a maddening pain.
I have a Kubota M7060. I tighten it with a wrench and it will still loosen after several hours with the 10 foot flail. Drives me crazy.
I wonder if two nuts would be a cheap better system. Like the way two nuts on a steel fishing rod reel seat rarely loosen. Only one nut on a steel reel seat is useless.