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I think primary chain is same but primary gear and basket gear vary
The primary shaft gear, the very large one the primary chain runs on is the same for the 500 and 550, they share the same part number, the smaller one which sits inside the clutch casing is different, the 500 has a 23T gear and the 550 has a 24T gear. The 550 clutch basket has 63T but the 500 isn't shown in the parts book.