I believe that they have picked up 7rwhp on an engine by indexing plugs. Read that in the Mathis Book. I indexed my plugs in my car. Not hard to do. Just a lil time thats all. I guess it really all depends on how bad do you want to be ahead. All the lil things can add up to a .10 or .2!
Mustang Performance Handbook by William R Mathis. Pg104
There is a very nice pic on that page as well.
1. Mark a line on the side of the spark plug's ceramic body indicating the open gap.
2. Screw the plug into the head and note the approximate degrees past the 12 o'clock position the mark is located.
3. Screw the plug into the indexing base and note on the index where 12 o'clock position should be in relation to plug in the head.
4. Select the thinnest washer that will allow the plug to screw in, under normal torquel and stop at the 6 o'clock position.
5. Note on the plug the cylinder for which it was indexed.
6. Follow the previous five steps for each plug.
In other words you want the open end of the ground strap to face the piston and the attaching point of the ground strap should be straight up facing 12.