Jack does this mean he has plugged all of the external vacuum ports on the intake manifold and run the engine with only the carbs as the air source? If so, and the valve timing is good, and the ignition timing is good, then yes, only the manifold to head interface could cause the problem. But if the brake booster is sucking air, then it makes no sense to remove the intake manifold, if you get my drift.
Good luck, and Happy Thanksgiving to y'all. We in Canada had Thanksgiving last month, as you know...