Here are pic's of my (first) attempt at a spreader bar. I took a short piece of 3/4" tubing and welded a 3/8" nut on either end. Then, I took two short sections of 3/8" threaded rod and welded a 1/2" clevis pin to one end of them. Last, I got two 3/8" wing nuts and threaded one each onto the rods, and then threaded the rods into the tubing. This works ok, but not great. If you could find a short piece of left-hand threaded rod, and a left-hand nut, then you would have something.... a very small centerlink for your 3pt hitch lol!
Here's a closeup of one end:
This one does the job, but the one knock on it is if when you need to adjust it for a different width of implement, you have to measure, adjust it by turning ONE END ONLY, tighten it down, and then drop it down in the pin's on the PEC. If you are off by a little bit, you might have to pull it back off and adjust it a few more turns. It can take a few minutes to do that.
I have plans in my mind for a second prototype that will involve two pieces of square tubing, one will slide into the other. All I have to do is round up some material, cut to length, and weld it up. I think my next one will work better than this one because I'll able to adjust the width a lot quicker.