Titus, I had a similar problem on the 444 that I'm currently working on. For your steering wheel to have a nut on top means its the older keyed type wheel, rather than the role pin. Somewhere in its past, I guess they couldn't get the wheel of mine, but they did get the nut off. Anyway, they just broke the plastic part of the wheel off, leaving just the metal hub. Then, they just installed a universal automotive replacement, as can be seen in the pics.
I was going to by a correct steering wheel for it, until I saw the lower steering gear on the shaft. It was really wore out. You can't buy the keyed shaft for these any longer, but you can buy the role pin style. It is a direct replacement, when used with role pin steering wheel. So, I just cut my old shaft off, and replaced it. You can buy the role pin style shaft here for $60. http://www.casegarde...stshrpinmo.html
I can't believe how much play this took out of the steering on this 444.
They also sell both the keyed, and role pin style wheels new, but their almost $100, so I bought a used one off ebay for $60. I'll take a couple more pics today of the new steering shaft installed, and post pics this evening.