Replacing Kuhn Tedder arm

I am in the middle of what I thought would be a simple project, but it is not. I am trying to replace a tine arm on a Kuhn 440 Tedder. The top bolt on the arm has sheared and I can't figure out how to open up the rotor so that I can put in a new bolt. Do I have to remove the wheel? The bolts on the other arms have me confused, too. They are stuck, but they turn. And they seem to tighten when I turn left. Then there are two smaller bolts under the disc, pointing up, which are very hard to turn. Are these the key?

I am about ready to start splitting and drilling out nuts, but am I missing something obvious?

Thanks so much in advance, as always.

Service guy at dealer: "I hate working on tedders. " I'm coming around to his point of view.

Replacing Kuhn Tedder arm