[Lynn Eades]

Tony, Rick etc. Not sure about Ford, but here's a little on Lucas.
A Lucas 6 volt generator will produce 12 volts. It will in fact produce 50 volts, (unregulated) but not for long.
a 6 volt genny can be converted to 12 volt by changing the field coils in from a 12 volt genny. This however does not work in reverse as the 12 volt armature cannot handle the current. The wiring needs to be heavier for the 6 volt.
This works because Lucas have built 6 and 12 volt generators using the same basic design. In particular I have been able to build a 12 volt genny for my carrier using the end plates and armature that came from a model of generator that was only ever built as 6 volt (original carrier)

On the Ford pulley numbers. Those numbers are probably just casting numbers.
A Ford part number is usually made up of three parts:
Here is a basic run down.
The root number (eg 10130) refers to a generator pulley.
The prefix (eg 01AS) which denotes country and year of origin and particular vehicle application. (I have no reference material to decode the 01AS. This may mean the part is specific to the Lynx armoured car)
The last part is the suffix (in this case a "D")
The "D" denotes changes or improvements in that item and so you might have a pulley that to all intents is the same. however they may have added material to strengthen the design, improve the air flow from the fan, or maybe even dynamically balanced as opposed to a static balanced original (just trying to come up with examples) Each time a design improvement is introduced, the suffix changes.
Someone like Tony Smith will be able to explain this in more detail.

I think Henry came up with a great system. If you have a war time Jeep or a CMP or a 1972 Ford Escort, the root number for an engine block is 6xxx It is the prefix and suffix that change.