Hi Chuck,
Of course you're correct. Thanks for posting the figure. The piece in my photos is an OEM Deere rear weight bracket, shown as #4 "bracket" in the left side figure of the parts diagram above. I have removed the part #1 "bracket."
I need a trailer hitch that's about 15 in off the ground. The factory hitch plate on my 318 is too low to the ground to be of practical use. I have read various conversations here and understand that given an overly entheusiastic ball hitch's bending load, the hitch plate on the 318 can tear the aluminum housing of the rear diff.
My plan is to incorporate the rock shaft into bearing part of that load as it does when heaped with suitcase weights. The tongue weight will be quite modest but the pulling load might be upwards of 1000 lbs. Given how the weight bracket bolts to the 318's hitch plate more closely to the diff than a ball hitch in the normal position, the bending moment on the diff housing is reduced. Further, since the weight bracket is bolted to the hitch plate in two places, effectively stiffening the plate, the hitch plate will rotate much less than it would with the ball hitch mounted on the end.
Thaks to Mike's measurement, it looks like what I'll do is scrounge up a hitch plate like his. I'll have welded onto some 1/4 plate that has four hole drilled to match the four in the bracket shown in my photos. When it's time to use the weight bracket, four bolts and the 120, 140, 312, 314, 317, etc. series hitch plate comes off and bracket #1 bolts back on.
Someone else long before me must have followed this same sort of reasoning to use a weight bracket for a trailer hitch on a 318. Unfortunately, despite some diligent searching, I haven't been able to find their work. I know that this is probalby a bit long winded but writing, editing and rewriting helps me think a problem through. Comments would be appreciated.