Take a look at the carb charts (from earlyer in this thread) and establish what kind of carbs you have first. Just because you have a 75 year bike doesn't mean you have that year of carbs on your bike. Knowing what carbs you have you can find the stock jet sizes, compare with the sizes that you are seeing to establish they are stock sizes. These bikes have been around for 30+ years and who knows who did what to them.
When looking for the jet size, only look at the numbers, the number is the size. The "geek" you are seeing is most likely the manufacture's stamp.
As fare as the "one size up" thing, i'm going to have to ask the same question from others here on the foam..
I may know the answer and not know it.
I know jets come in .2, .5, and 1+ etc.. increments, for example, 135.2, 135.5, and 136.
Is "up one" jet size the first point scale (135-135.2) or the full one size up (135-136)??
I'm sorry, i really should know this...
hope i could help