I'm not sure if you've seen this post.
http://www.tractorbynet.com/forums/build-yourself/118976-quick-hitch-made-my-own.html
At first I assume that he had used solid stock. till DAH I looked at the picture and saw just what he used.
I wouldn't abandon the idea , Al tho I haven't welded yet i have put-sed around some with ideas.Such as how its welded to the top of the link . I am not sure that it needs to be a "J"
I envision just two separate pieces of stock welded in the vertical to simulate the hook. the pin could either rest right onto the original arm metal, or I cold weld a small piece of metal to the bottom. (all this would eliminate the problem of cutting the "J" from heavy stock)
Th retaining pin has always been a concern as I didn't know the width of the stock that is used on the carter setup or the pin size.I assume its not need to be a large diameter.
Thanks ! I had Not seen this thread...
I made the "J's " by drilling a 7/8 inch hole in 1/2 inch stock then using my angle grinder with cutoff wheel I finished it ... not that hard to do

Using 1 " stock would have worked much better but all I had was 1/2" so my retaining pins had to go on the outside.
bob