There is no real reason to index(except to see what it does for your motor ) the spark plugs in most stock type SB Mopars, the plugs are almost up in the center of the combustion chamber(like a Hemi )so the ground electrode is not in danger of hitting the piston, like it can in BB and SB Chevy and Fords with dome pistons I use to do that in my 426 M.W. NHRA stocker with the high compression pistons(13.5 to1 comp. ratio). I would try to point the gap opening at the intake valve, it is a lot of work and really no measurable gains to be seen