Dave,

   Re:

I am thinking that perhaps the Constant Speed Controller could take a pickup off the Crank Position Sensor for tach sensing as well. It doesnt need to be a strong signal.. just a signal. Just a thought. The Crankshaft positions sensor will give a reading regardless of injector disable or coil disable settings.

Run it by him and see what he thinks...

    If all you need is a steady predictable signal, why not mount a
hall-effect transducer next to the ring gear of the flex-plate?  If the
timing between the pulses gets shorter the engine is going faster;
longer, the engine is slowing down.

Dale R.