I guess England believed in more operator controls than American companies.

My 1930s American car has no operator controls to change the charging rate. And I think that was typical of many/most American cars. You opened the hood and adjusted the location of the third brush on the generator to set the charging to be about right on average. That meant seasonal changes (more lights and a higher starter requirement in winter than in summer, etc.) and for the type of driving the owner typically did. Basically this system was used because it was cheap and almost adequate, not because was technically good. If they were going to add controls to adjust the charging it was just about as easy to put a voltage regulator on the thing. Which they started doing just as soon as the accessory loads (radios, etc.) and increased lighting loads made the third brush systems woefully inadequate.

If your driving pattern is a number of small trips (neighborhood check out drives, etc.) with occasional long tours then you will be forever twiddling with the third brush adjustment. Or you will set it on the high side for the short trips and then run your lights on the tours.

But you can hide a electronic regulator under the cover where the judges can't see it and forget about actually using the third brush. Works for both long and short trips. Summer and winter. Day and night.

Some things to consider.

The 3 brush generator with cutout uses the battery as the voltage regulator. The problem is any resistance or loss of connection to the battery will cause the generator voltage to raise. A loss of connection would cause the voltage to spike upwards of 60 volts burning out any light bulbs.

Modern technology has caught up and a touring car should put in a voltage regulator. It seems many are available that just fit in the generator and keep the voltage and charge rates appropriate.

Alternators are not needed, unless you are installing some big accessories like A/C. In the early cars the alternator could not put out high rates because the belt just can not be made tight enough. This is especially true on the Model A. Keep in mind how we used to adjust the belt on an alternator. It was considered too loose if you could turn the pulley with your finger.

For bulbs get the Australian made halogen bulbs. They are direct replacements for original bulbs and use marginally more current. They will give you a bright light, even with bad reflectors, that will allow you to drive 55 MPH at night. http://www.welcome.to/cvb

The ammeters in the cars can be way off. Just because it shows 10 to 15 amps does not mean that is real. You may want to confirm this with a known correct ammeter.