Re cotter pin: Actually now come to think about it, my SB45 doen't have a ground flat on the output shaft just a keyway like yours.
It is not a cotter pin like on pushbike cranks (if you can remember them) but rather a half threaded 3/8" pin with a semi circular cutout that clamps the output shaft when you tighten the nut up, a better way of holding the clutch as it won't leave dimples like set screws will.
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