Does this carb have the foil tag that says Competition Series on the front? The first series of aftermarket AFB's were 9000 Series-that is what you have, I'm pretty sure. The Competition Series came just a little after that. I have a couple Carter Performance Products books from 10-1975. The 9000 Series has the 400 but the Competition Series starts at 500 cfm. From what I've heard, the 9000 series are better carbs that the Edelbrock Performer series.