NOS carburetors. What issues to be aware of if any?

Nothing runs like a new carb—a real one, not the Chinese copycat trinkets.

In theory, you have to be all worried about old gaskets and stuff.

In practice, better than 9/10 times all you have to do is use an unbent paper clip to carefully push the inlet needle off its seat (they stick with years of sitting on the shelf), install the carb, spray some light oil—WD40 is fine—into the carb bowl through the internal and/or external vents and operate the throttle lever a few times to lube the accelerator pump plunger, start the engine, and make your adjustments.

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.