To get that wheel off try the following:
Take the nut off
Spray the shaft area with a good penetrating oil like PB Blaster, Kroil, Deep Creep...
Let it set for a few hours and then spray it again.
Put the nut back on flush with the end of the threaded shaft. (You don’t want the steering wheel to be able to hit you in the face when it lets go of the shaft)
Sit on the tractor seat and press your legs up against the steering wheel so that you can use your feet and calf muscles to push up.
Grasp the steering wheel rim and jerk up on it.
Hopefully the wheel comes loose and the nut stops it.
If not spray the shaft again and wait 24 hours and try again.
Spray and wait and try and spray and wait and try
The shaft is tapered so hopefully no one over tightened the nut and pressed the wheel too hard.
If all else fails the try hitting the nut while pressing up on the steering wheel.
The you may have to cut the hub through the side to get it off.
I think the l185 or L225 wheel would fit.