Garry right on. I would index the plugs on the race engines. Would point the ground electrode as close to the center of the intake ports as reasonable. Usually in a range of 25 degrees up and down from center intake port. Wanted not to shadow the fuel charge with the electrode pointing toward the exhaust side.
Foot Doc – yes it was and is fun. I read about plug indexing in a performance cycle mag back in the early 70’s and did it with the race engines then and now. With the L61Y I would also open the gap as wide as possible (like 0.065") and not strike piston , could do that with the CD ignition with a lot of fire power in the system. Also tried cutting the ground electrode off so only a vertical electrode piece remained so the spark was completely to the side. Ran good no loss in performance, but a bit more difficult to start, so for racing wanted start reliability and never used the side spark at the races.