For a 1962 Mercury Mark 25 Champion J6J and J6C—–> NGK B6S part #3510 also NGK BR6S part #3522 a resister plug if you need that?
Check gap and either plug should be 0.025"
These NGK plugs are standard heat range equivalents to J6J and J6C and should be ok for general service use. The J6J and J6C are the hottest Champion plugs in the J series, J4J would be the next colder. You may require a colder plug depending on conditions of use and are available in NGK like B7S is one step colder. Higher numbers in NGK are colder the opposite of Champion numbers.
Edit: Ok Dave if year in error, he should just focus on the plug equivalent NGK to the J6J and J6C which was noted by Chinewalker as the plugs for the engine.
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