You might get some flat iron stock or angle iron...I think home Depot and Lowes carry short lengths......
Drill the iron so that you can bolt it up to the u-bolt holes on one arm of the yoke...then I'd hold it and hit it with an air or electric impact tool, or you might be able to use a breaker bar... I'm guessing you have a socket.....I don't remember the size, but O'reillys carries individual deep impact sockets...measure the nut in inches and millimeters and they may have the size in one or the other...heat always helps...cleaning off the threads will help also..