So it really does seem like motorcycle oil is part science, part religion, part bullshit.
This oil, Castrol 4T 10w40 JASO MA-2 Conventional Motorcycle Oil is what I got cause I know the bike will run on it, and the crankcase says to use it. Also they come in convenient Liter bottles so we don't have to buy an extra bottle just to make up for the slight difference. Maybe next time I'll use Rotella 15w40. Maybe.
At least I'm done with that part, for now. Time to deal with the mysteries of Moly 60 Grease, drive shaft splines, and rear tires.