Simply ohm the tip to electrode to make sure it is not a R plug.
Best F8DC4 replacement for 104 Waste Spark Ign [ DIS] systems is NGK BCP6ES.
Copper core/non resistor.
https://www.summitracing.com/parts/ngk-4930
90% of fouled plugs/skips/misfires on 104 waste spark systems is caused by the Resistor boots on top of the plug, not the plug . Good idea to change these 3 boots whenever changing the plugs on 104's ................