When I worked at the farm, we converted a Ford 9N 6V to 12V service. The owner had been having problems with cold weather starting and felt that 12V would give it some additional energy for starting. (which it does certainly by putting 2x the amount of energy into the same battery envelope as it is twice the voltage.)
The tractor had a generator which was "two wire" as I recall. (no third brush and one wire coming out was the output and the other wire going in was for the field.) The only change to the tractor was to change the regulator to a 12V regulator and -voila the machine was instantly a 12V generator.
I looked it up on the Internet (wot a tool this Internet) and confirmed my statement.
9N tractor circuit diagram above. The wiring coming off the right-hand side of the generator and connecting to the voltage regulator is the ground shown diagramatically. The other two wires are output and field supply.
We made no other changes to the tractor and used the existing drum type bendix gear without issues. Well, it would "slam" pretty hard I thought compared to before, but the owner thought the drum bendix was equal to the task.
We'll have to see what KevinMac can offer further for information on his spitshine generator but something like this may have been where his prior owner was headed.
It is a more conventional setup - used post WWII until alternators became standard after the invention of diodes.
Joe K