1. i would look in the factory parts catalog for jetting before sterlings website, his chart might not be accurate.
2. an 85 GS should have a 12A in it. there are a couple flavors of 12A, but a 4 belt pulley and studs on the front cover probably mean the engine is the correct one.
3. there is a page in the factory shop manual,
www.foxed.ca on how to do a tuneup, like setting the idle mixture and timing, you should start there.