The steering arm is keyed at the top so you cannot drive the shaft down out of the steering arm and spindle tube. The best way is to unbolt the tie rod from the steering arm, unbolt and remove the entire front end spindle tube assembly from that side, turn it upside down and put it back in the center tube. Then heat the steering arm up with a torch and use a hammer to drive off the steering arm. Hammering down works MUCH better than trying to hammer up.
The spindle bushings are available from AGCO dealers or aftermarket I believe (e.g. A&I). When you go to put it back together after putting the new bushings in, put the spindle in the freezer overnight. Heat the arm back up a little and drive it on the frozen spindle, should go on much easier. Of course have the spindle housing back in the upright orientation for reassembly. HTH. Mike