An alternator produces electricity and a regulator regulates the amount of electricity it produces.
Which is better and why? I don't understand your question. They are used in conjunction with one another.
Whether the '55 engine is 12V depends on if it was from a car or a first series or second series truck.
Your truck can easily be converted to 12V if you want 12V wipers and radio. You can use either an alternator or generator. A generator will be fine with just those accesories. If you go to adding things like A/C, power seats/windows and the like, go with an alternator.
