Or he could just hook it up to the draw bar with a pin, like God intended.
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I don't have a better "draw bar picture" than this, but OP, it's sitting down between the lower link arms, and currently has a clevis hitch in it. You can extend it out, it's currently pushed in all the way.
I would never hitch even a moderately weighted trailer to my 3 pt. That's what the draw bar is for. Can get one at a tractor supply store if your tractor didn't come with one. Mine didn't come with a draw bar, but I bought one from my selling dealer when I bought the tractor.