? on plugs for a 350cc Yamato

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Hey guys I'm finished rebuilding my Yamato 350cc alky (RB4) and need to know which plug to run in it. The manual gave me three choices. They are NGK B-10HN, NKG B-10HV or Champion L-87R. Which one of these plugs or there replacement can I still get. Or is there a better choice of plug?

Thanks,
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