After listening to lots of good advice on this forum, I'm looking into changing the distributor on my '54 Merc to something with centrifugal and vacuum advance. If I retain the Holley 4000 carb, where do I get the vacuum to drive the vacuum advance. I'm assuming that the existing vacuum port on the carb with the spark control valve will not allow the proper signal. I'm thinking of a '58-'64 Y block dist., or a modified 289-302 type, but as I recall they didn't use full manifold vacuum???.  Thanks : Bruce