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

Depending on the year the NOS carburetor was built, it could have been sitting on the shelf for up to half a century. Slantsixdan is on the right track, just if it were mine I would locate & purchase a rebuild kit just to have on hand in case it needs a rebuild. That way if it leaks, you have the kit handy instead of having to scramble around trying to find one.