"63 Impala booster leak issue

Just recently did a more than a complete brake job on a 1963 Impala. New everything including steel lines. My problem is when the master cylinder is installed on the booster, I get a vacuum leak. If I put the old cylinder back on there is no leak. The cylinders are identical, and all my research has shown that power and non-power use the same cylinder. Any advise would be appreciated.