Wow! That's the first kit I've ever seen. Good to know that someone carries an armature but again, don't buy one unless you need it.
Brushes (here) are US$6 per PAIR at Rock Auto. Generators used a couple different size bearings depending on if the gen was heavy duty or not.
The way to do this is to take your gen apart, clean it and inspect. Bits of highly conductive carbon will cover the inside along with road oils. I use diesel fuel to clean mine, then gently blow it dry.
If you need anything, measure the old part and order the same. The only critical part is the commutator. You want to catch worn or stuck brushes before they ruin the copper segments.
While you're at it, do your starter motor. Same drill but you can order once and possibly kill two birds with one shipping charge. - Dave