Get yourself a fancy timing set
It will allow you to run the sprocket 2 degrees retarded, dead on, or 2 degrees advanced, depending on which keyway you use
That should give you what you need to time it right
Ok! Just looked through my parts and I actually do have one of those crank sprockets with the three keyways, and can see the +/- graduations on it. Now just have to get a degree wheel. Thanks