Jerry,
Are these new headers and intakes? If so, they do not correctly bolt-up together unless you grind off a little metal where the intake rides against the exhaust (I dry fitted and kept grinding, mostly off the intake, until I could slide a piece of paper between the manifolds). I used the intake inserts with no problems.
This problem will result in the exact situation you describe - an intake/vacuum leak.
If these are new and you bought them together from the same vendor, I would have expected them to provide a warning about this situation.
Try a search on "Offenhauser Fenton" in this forum and you will find a few discussions on this topic.
Tim
