My round tube draw bar mounts like these photos for the round one show. But the bottom of my case is not recessed ad your tractor pictures show. I wonder if yours used more of a flat stock draw bar.
Threads are most likely a standard metric thread. Clean them out measure depth and diameter, get some 3/4 or 1” bar stock and make your own draw bar if you want one.
Measure the width and length of that slot. Allow yourself about 1/4” of play on each side for with of bar stock. 2.25-2.5 times the length of the measurement of the recess slot.
Make a cardboard pattern an mark the holes. Drill or have some holes drilled for mounting holes. If you want the 2 plate mount like in the round stock photo above, let me know and I will take some measurements of mine and post for you. Or you may not want anything there and use a 3ph drawbar.