I'm not sure if this fits in your plan or not, but since you're messing with adjustable ignition systems (I'm thinking without knowing that your bike has adjustable ignition timing), most newer (and not terribly expensive) timing lights have a built in digital tach, just picked up from the inductive pickup.
Dunno of that fits your plan or not, just throwing it out there.
That's good to know. Thanks! The timing light I have is just an old Sun advance timing light. It doesn't check rpm. I kinda want a coil fired tach. Easier to work with. But I guess a wire wound induction pickup works too.
It just feels like my engine is running slower than suggested at high speed. Maybe not.