Squareback vs round back alternator?

Yes. Usually only the part number. Specs will be in your shop manual.
The most important part to find new old stock will be the distributor points and condensor.

I can check that against new 1960s shop manuals.

View attachment 1715890184

Other end of repair positive wire should connect to ballast resistor. Where that is located, I don't know.

The ballast resistor is missing on this car. So I ordered one and once it's installed on the right place we'll check with the tests you suggest earlier in this thread.