Ron the single ignition was one of the newer BTH mags, and the twin plug was the Grosset ignition which is one specifically for a twin plug engine, that is it has about 12 degrees of advance in the ignition unit itself. I am not sure of their advance curves but I'm sure it must be published somewhere. The 600 Comet with the Grosset twin plug set up (Terry Prince top end kit) was inclined to still ping a little under load, so i set the ignition to 26 full advance and we run it on 95 Octane fuel, this engine runs a 36 mm pumper type dellorto carb in case you are wondering, it runs very well and loads of power, enough to make the clutch slip.......