You'll get a wide variety of opinions on spark plug resistors.
Some believe that no resistance gives a hotter spark, some believe that some resistance - about 10K total seems to be suggested - gives the best ignition since the spark lasts longer because of the resistance.
I don't know either way, they fire the mixture the same in my experience.
I use 5K caps with metal core wires, for 10K total resistance per plug pair. You can measure the resistance of the wires, graphite core can be very low or fairly high resistance depending on the chemical mix in the graphite. If you have 5K or nore per wire, don't use resistor caps. If it's very low use 5K resistor caps if you have them, or buy non-resistor or resistor ones depending on which theory you like.
If you have resistor caps and want non-resistor ones, try disassembling them and substituting slugs of metal for the resistors. The metal part that attaches to the plug - inside the plug end - should have a screwdriver slot in it. If it does then it just screws out and the resistor just falls out from behind it. A lump of metal roughly the same size can be substituted.
