I made a purchase ass-backwards. I bought a 4 pack box of Bosch WR7DC spark plugs, then read Snow Bums article and he recommended against using any plug with the "R" letter, meaning it is a resistor or resistance plug, not to be used in airheads. My 1992 RT owners manual recommends Bosch W7DC. Do I now own 4 paperweights? Thoughts please. Thank you!