ALWAYS replace the cam gear with a chain job. They will wear out the chain quickly if not done.
Then add an offset key if needed. Remember, half the key. IF you have 10 degrees stretch, you need a 4 degree key, max. You are better off to have too little than too much. 4 degree key = 8 degrees on the crank. This will leave you with 2 left over, this will be fine.
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