Johnnie,
Since you're asking this question on a Concours Forum, and prefacing it with a statement like "I just want my car to be correct.", I'd venture to say that the issue was important enough to you to try to find a period correct air cleaner. That being said, the issue of whether a correct air cleaner for your car should have a snorkel or not is a little more difficult to answer. Based upon the limited amount of Sprint owners that participate on this forum and the date of your car, an air cleaner without a snorkel is the probable choice. But Ford in those years rarely did anything in a cut and dry manner, and there are allot of Sprints and 6-cylinders unaccounted for if we merely poll the participants here. We may find that snorkels were used in some instances.
I think Dave's suggestion is probably a good one: Paint the air cleaner you have, and keep your eyes out for a dated base. Or you may attempt to reproduce the stamp in the base, and just keep the whole thing. Sorry if this is a vague response, but there's no way to advise you differently without researching the thousands of 6-cylinder cars built in '66. Keep what you have and begin noting what you see a car shows. Talk to Tony Kovar who runs the Sprint registry. He may provide a little deeper understanding from his personal forensic experience. I think it was his comment about the late model year change over that you're referring to. Just be prepared that there may never be a hard fast rule....
