your right Knight, it does look like the "unamed" hitch you posted. I pretty much copied the design, BUT changed some things for my tractor. The upright on the "unamed" hitch is too long. I measured the vertical distance from the lower lift arm pivot to the upper lift arm pivot. I made the distance from the drawbar pins to the upper link pin this distance. I also measured the horizontal offset of the lower and upper lift arms on the tractor. The lower arm pivot is placed closer to the front of the tractor than the upper pivot by about 2". I build this offset into the hitch also. Now when I raise the 3PH from lowest position to highest position, the ball stays level. I guess these dimensions may change on different tractors, so measure yours. After making your plan, check to see if your upper link will extend out far enough to reach the theoretical distance. Mine did, but not by too much. Also, make sure your 2" hitch insert slides into the larger tube before welding. I bought a 2-3/8" O.D. square tube with 3/16" wall thickness. Take it from experience, a 2" tube will not slip inside this large tube because it has an internal seam. Also, I think the 2-3/8" dimension is held tight in manufacturing, but the 3/16 wall thickness is not (but you'll still have a seam on the inside). maybe someone knows the exact tube to purchase. I bought a new bolt-on step bumper receiver hitch from a discount surplus warehouse near me for $5 and ground off the welds on the mounting plate so I could use the tube. The rest of the steel was free, the drawbar was $18, and the two grade 8 bolts, nuts and washers were about $2 total.
One last thing, if you read about the "unamed" hitch any, you'll see that they recommend a chain be fastened from the top of the upright to the swinging drawbar. On uneven ground, the 3PH will raise up (remember, no down force on 3PH, just gravity-down). Both on the "unamed" hitch and mine, there is a slot for a length of chain to slip in. 1/4" chain would work fine here. You would attach the other end to the swinging drawbar with an eye bolt. Your pic shows this. The excess chain would just go into the upright tube.
