Carefully support the front frame casting in a vice etc. with the armature hanging down. Thread the drive pulley nut loosely onto the shaft, then tap gently the end of the shaft with a brass hammer. The armature should slide out of the bearing. If it does not GENTLE heating of the shaft above the bearing can help loosen it.
Once the armature is out remove the 3 screws and the bearing retainer the frame casting. The old bearing should then drop right out.