The instructions in the link look pretty good, but I didn't read through the details. The kit should have included the bushings for the drive-end frame and for the commutator end frame. If the kit provided the complete commutator end frame, better yet, because otherwise you have to cut the old bushing with a chisel to remove it-- and with that, it often doesn't get replaced. The drive end bushing can be driven out with a punch. Drive both bushings in with bushing driver if you have one, or use a wooden dowel to install them, being careful not to distort them. They are both oilite bushings, I believe, but give them a few drops of oil anyway, or a little lubriplate grease.
You can use an ohmmeter to test the armature for grounds and test the field windings for continuity and ground, but don't try to remove the field coils. If removing the field coils is necessary, take the starter to a rebuilder. Resistance in the field coils is very low, so don't be concerned about only a couple tenths of an ohm resistance measured with an ohmmeter.
If there is a large leather washer in the kit, that is a thrust washer for the commutator end of the armature. Some kits don't include that, but it should be replaced, and the new one oiled somewhat freely when installed.
The kit should have included the shifter fork and drive. If it didn't come with the fork, you should find one and replace the original- they develop a wear pattern that looks like the normal shape, but any flat surface on the fork bearing surfaces is wear. Same for the pivot bore.
The shop manual shows the armature being tested with a growler for shorts and winding consistancy, but you probably don't have one, so you have to go on good faith or find a rebuilding shop to test it for you. In which case, you should have them do the rebuilding for you- they will turn the commutator, which you probaly can't do, unless you have a lathe or an armature tool (lathe). If the commuatator doesn't appear to be badly worn, and there are no loose or burned bars, you may be able to do without turning the commutator. If you have the commutator turned, one way or another, the insulating mica between the bars doesn't get under-cut as it would be with a generator commutator. But a rebuilding shop would know that.
Getting the retaining ring off the drive end of the armature shaft can be troublesome, but you can usually get the ring off by tapping it with a punch, or use a deep socket or piece of pipe that fits the retainer diameter. Then comes the lock ring; snap-ring pliers may work to expand it, but usually you have to work the ring out of the groove with a screwdriver, but it is tempting, and easy, to drive it downward- toward the drive-- wrong direction. Putting those rings back together is not so bad. The shop manual shows a picture of assembling the retainer and lock rings.
All I can think of right now. Hope this helps.
Harvester