Just as a general point of automotive evolution, third-brush generators were a thing of the past by about 1940... the "modern" automatic three-unit voltage regulator was being employed by the big three, and most other mfrs, and generally worked very well, tailoring the generator output to suit varying load demands (headlamps, heater, radio, etc.).
This was a solution to changes in vehicle demands (more electrical demands) and owners' driving habits (more night-time driving, longer driving over improving highways).
The mechanical voltage regulator served well, and survived the transition to the 12-volt era.
All that said, a properly functioning 3rd-brush genny & cut-out still works as well today, as it did in 1928... and it still will not automatically adapt to varying load-conditions.
Since there now seem to be options to upgrade the stock Ford gennys (both Powerhouse and "Long-frame") with modern voltage regulators (tastefully disguised / concealed), they should function just as well as a 1940 or later generator system.
Personally, I have been driving old iron for some 30 years now, most if it six-volt, and have never been compelled to change-out a generator for an alternator. (Or convert to 12 volts, for that matter.)
My '28 Special Coupe does have a 6-volt postive-ground alternator in it, but it came with the car. It works, so it is staying until I run across a stock genny at an attractive price...
If I had a decent Powerhouse, I would probably spring for Tom's concealed EVR...
Cheers,
SC Frank