JH, I would run the 9's unless it fouls plugs often, Then I would try the 8's. The R is a resistor plug that cuts down interference to electronic equiptment. You have a 1979 I don't think it will matter much if it has a resistor plug or not. With todays newer sleds it is HIGHLY recommended that a resistor plug is used so it will not interfere with the computer (cdi) of the sled.
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