as far as I can find NYS makes no exemption for antique vehecles that aren't requirwed to have seat belts.
Was pulled over a handful of times in a '60 Pontiac with no belts - once because the cop couldn't see the registration and inspection stickers over on the side of the wraparound windshield (where I have seen them as far back as NY has used those stickers, on those cars). Never got a seat belt ticket. Live in New York.