I know how zeners work, but not completely following your logic of using a 36v zener. How is that going to be better than using a voltage divider? I'm leaning toward adding a variable resistor or pot to fine tune with.
I'm not 100% certain this pipe dream, which isn't mine, will work without frying the exciter/armature/rotor/voltage reg, or the entire alternator.
Also been thinking of applying full 12v to alternator and controlling it with the RPM's of engine.