I've got a couple of Nos AVS carburetors that are still in their original boxes, clean and in perfect condition. Is there any reason I shouldn't be able to just bolt them up and run em ? I haven't decided which one I'll be using, but since they are 40+ years old, I'm just curious if anyone out there has bolted an old Nos one up and had it work out. I'm thinking it should be fine. Opinions?

They should run fine. Only issue I can imagine is that the accelerator pump might have dried out since it is leather. You might be able to rejuvenate it with a soak in some ATF. Only a quick disassembly would confirm that.

Agreed, should be fine but if not you won't know without a test run or a tear down. The acc pump or the needle/seats being dry or sticky would be the trouble areas in most cases.