Many years ago I had a similar problem: I would lose my spark after about 100miles, I would fit a new pair of plugs, manage another 100miles then same thing. After about half a dozen pairs of plugs I pulled the mag. off and there was an almost invisible crack in the slip ring. New slip ring fitted and I then had six pairs of good useable plugs!
As your mag. has now been rebuilt is it not worth trying your old NGK A6 plugs again?
Rod
