What Dirk said is accurate, however it's not without exception, I've seen th earlier style on original later carbs as well. Also keep in mind that they are easy to change out so in many cases it's hard to say which they had when new. Some other non Mopar Carters (GM, etc.) had similar choke bases & housings which will bolt on and work but have minor differences in the casting shapes, however, some won't accept the other componants. It's possible that you bought one from a non Mopar application.