It'd probably be easier to use someone else's picture, and take some parts away, LOL...
Imagine in the picture below, without the jackstand, and wheel. I had more in mind of it standing more perpendicular, but basically that type of mounting.
Now, imagine where the bracket goes back to mount to the cultivator frame, instead of being routed out like this one is to fit a square box tubing, it would be in a V shape. What is missing in this picture is the piece of angle iron you would fabricate, to weld it to. It would lay right over the front of your frame. Holes drilled at the point of the angle (center), so as to bolt through your frame. Bolt holes would be drilled outside the width of the brackets going back to the frame for easy access.
A piece of angle iron the same width, or two shorter pieces for on the backside drilled to accept where the bolts come through the frame. Basically sandwiching the cultivator frame.
At the bottom of the leg, where the wheel would attach, you could make a couple similar brackets that attach that jackstand. Understand that that jackstand is mounted to an outside piece of tubing, and the foot of it is mounted to an inner piece of square tubing on that to get it to adjust.
If using like a mower gauge wheel, make the similar brackets. Make them come out in front far enough to align bore, and slip a piece of round tubing in those holes for your sleeve to hold the stem of the gauge wheel.
Note the multiple holes drilled in the bracket, and leg for adjustment. I would use two bolts, or pins to keep it from racking towards the back. The cross piece across the face, between the brackets would stiffen it greatly. Shim the bracket an 1/8" or so wider than the tubing when welding together, to allow for easy adjustment when finished. Using small like, drawbar pins would make for quick and easier adjustment. But bolting it would eliminate a lot of chatter I'd imagine.
I still believe I'd run a brace back to the center section, off the leg. Pieces of flat bar stock wider than the framework, and utilizing the 45 degree angle it would be headed back towards the bottom of the leg, towards the wheel. They (pieces of flat bar stock) would be wider than the framework, so as to allow room to drill holes to sandwich the framework to hold it in place. Adjustment of the angle when cutting the brace bar may be needed to get it to come out where you want it. If the brace piece was cut on a 45 degree angle, however far back the middle cross frame is from the front, would be the distance the brace would be from the top of the front cultivator frame to the bottom of the leg.
And again, if using some mower gauge wheels, most of the stems are long enough that spacers are used top and bottom for fine adjustment.
The only reason I suggested the mower type gauge wheels, was for the pivot action. I have no idea how large your arena is. If it is large, guess I was thinking of doing the center section in straight shots, picking the cultivator up when you turn. But finishing the outside, in a long sweeping turn. Here again, not sure if you have a large round pen arena, square or rectangular. Even at that, if you don't drive perfectly straight, it may tweak on the cultivator framework if the wheel doesn't pivot some. There's going to be a lot of side leverage on that long of a leg.
Then again, you could just do a similar thing as in the picture, but guessing you'd have a couple hundred dollars in materials alone.
Clear as mud now..., Eh..??
View attachment 298795
Good luck with what ever you decide to do..!!