+100 Back when I used to spend ridiculous amounts of time and energy trying to eek out every ounce of horsepower and performance from anything with an engine I owned, indexing plugs was always part of the process. I would use copper washers to shim the plugs to get my angles right. I made some washers last week for the HimalayanIndexing can make a measurable difference too.
That is, when fitting the plug trying to make certain the gap on the plug faces in towards the centre of the cylinder.
Both plugs incorporate a resistor so a resistor cap is not necessary, but suitable caps without a resistor are hard to find.