i am not sure about those two things in the picture, but my guess is they are a fuel stop setting and a fulcrum setting for the governor, actually they likely both work with the governor. as such i would "not" mess with either of them.
especially without knowing more about them, and having a manual in hand for the engine.
sounds like you got a good runner!
now the brushes, again i don't know the length they were as new
but st heads are famous for one brush wearing faster than the other, same for the slip rings... so if both brush sets are about the same length, and the slip rings look about the same it is likely the thing doesn't have a lot of runtime hours on it.
and i wouldn't change the brushes unless they are running short enough to look like the springs are close to limit or contact the slip rings.
do you know if it was stored under cover? if so that would be a plus.
i would clean up the slip rings and see if you can get it to generate some power, maybe a 100 watt light bulb to start with.
if you can get it to make power, and you see signs of water ingress, don't run it for long or power much of a load. i would then take it all apart, have the stator and rotor tested for shorts, and if they test ok, maybe have them baked dry, vacuum dipped and baked to set the varnish. a good motor shop could advise you on that.
you just want to make sure that the thing is clean, dry, and has enough varnish to set the windings, and protect or insulate as well as you can. if you take it all apart and take the stator and rotor in for testing and bake/dip/bake... it shouldn't cost too much, the motor guy could tell you if it would be worth doing or not.
then either replace or repack the brgs and reassemble, i would replace the brgs, but that is up to you.
it might have a failed rectifier, which is not uncommon, and easily upgraded for not much money.
it is really so hard to diagnose or advise from pictures, pictures can make things either look dramatically better or worse that what they really are in person.
my bet is the old girl doesn't have a lot of hours on the unit, and it might well be the rectifier gave up and that is why the generator box was apart and the thing sat around unused up till you became the proud new papa and brought it home.
i am not sure if the engine is a s195 or an s1100, the s1100 being a bit bigger of course.
if you have an 1100, you did well, i wish i had scored one preban, iirc the 1100's were direct injected and used a ball brg on the flywheel side of the crankshaft to carry the load, common for an 1100, less common on the 195's
sounds like you got the start of a good project.
and in my opinion once you go changfa type your hooked for life.
(me) "my name is bob, and i am a changfa addict"
(group) "hi bob!"
bob g