I've got two of 'em, one in my car and one in my parts bin. I got the one off a 78 Lincoln Versailles so I'd say it's a good chance it was stock. I've seen a few that aren't but I've had at least a half dozen that are adjustable so they do exist. I actually found this out from a guy at a speed shop when I went to buy an adjustable vacuum advance, he told me to try it first and because of that he lost a sale

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