After getting the "J" hooks like I wanted them I had to figure out a latch mechanism. I think that what I did will work well--time will tell.
I attached an arm on the latch which extends inside the frame. To that arm I attached a rod that extends out the top of the frame and I capped it with a knob that I can push down on to force the latch into lock position.
The latch can be held in the open position by the little pieces of pipe that will just clear the top of the frame when the latch is fully open. It is simple and it should work--I think.
I tried it out with my simple 3 pt ball hitch for a utility trailer and it seemed to work well, so far.
Now I have to make a top hook and fabricate the tractor side. Maybe later in the week I will get to finish it.
Mike