Question about plug indexing
Here is some interesting reading. I've never noticed a difference, but I never made any specific back-to-back comparisons. My opinion is the same as Jacobs - It might help, and it certainly can't hurt! I index a new set when I feel ambitious. But I go through a couple of boxes to get the correct orientation instead of using washers.
http://dodgeram.org/tech/gas/spark_plugs/s_plug _indexing.htm