Correct SC Spark Plug
 

Porsche parts dept. didn't have spark plugs for my '78SC, they sent me to a local store.
Factory recommended plug is the Bosch W8DC, but store didn't have those either. Cross reference catalog recommended the Bosch Super WR8DCW (stock #7506). The store owner said he sells a lot of these to the dealer when they are out.
I can find no reference to this plug here, or Google either.
Anyone have further info before I go to the trouble of installing?

You can use NGK's too. Asking which is better is like asking what brand of oil to use. Any auto parts store can look up which NGK's go in an SC. I don't have the part # handy.