If you want to do something to the plugs to help - round off the corners on the end of the grounds - this will eliminate hot spots. Also keep opening the gap until you get misfires and then tighten them up.

I've done both of these things to my car and made a nice little difference KR wise.

Indexing spark plugs is an old racer trick. The conventional wisdom is to face the opening of the plug at the exhaust valve, not the intake. The idea being to start the burn in the potentially hottest part of the combustion chamber, thereby lessening the potential for two flame fronts in the chamber. Shims in various thicknesses are available from Jeg'* summit and others. It can be a tedious process to try various plugs in the cylinders to see if a shim is required or not. Knocking the corners off of a conventioanal plug are also a good idea as mentioned.