If there was no overvoltage the regulator contacts would never operate, they reduce the voltage to a preset threshold.

Now we are arguing over semantics . The regulator will work when the voltage reaches a set limit . whether you want to call this an overvoltage is up to you . Qn a 12v setup the CVC is set at about 14 and a bit volts , so as to charge the 12v battery .

My safety valves lift at a set pressure in the same way , but I don't call it an overpressure , unless they are set wrong .

Looks like an awful lot of trouble to reinvent the wheel. Just a variable wire wound resistance is all that is needed in the field and keep your eye on what's going on.

Except that Uncle Joe Lucas , Prince of Darkness , made millions of the things , and modern , smaller solid state equivalents are also available . So perhaps not so much reinventing the wheel , as using one off the shelf .

I think I would start with the basic unregulated circuit first to see what is attainable.

I would connect terminals F and D together so full potential should be available between terminals F/D and the body of the dynamo. (see circuit post 18)

I think using a variable wire wound resistance might be much the same as controlling the engine speed manually.

I would also check out bulb availability and investigate the dynamo’s output at 6 Volts.

use a bike reg from john goff cant remember his website small solid state and reliable he does ones for dynamos and alternators inc dynamos with no battery