If your pinging was due to preignition you don't want to drop octane in your gas. My 98 Mach manual calls for high octane fuel so that's what is run in it. What quality comp tester did you use? It might be worthwhile to borrow another one and compare numbers. The reason the plugs are gapped so tight is your stator is the same as a twin stator and you are running 3 coils not 2 so spark is not as hot. Donnie over at Dootalk has hi performance coils that let you open the gap up. You can build your own with Evinrude coils but it worked out for me to be a better deal just to buys his than build my own. You can do a search over there in the Mach 1/Z tripples section for info on both.
As Red Green says "Keep your stick on the ice." Thanks Mike