My 67 formula S 273 had California emissions which was a green vacuum pod that had three ports... One went to ported vacuum on the carb, the other to intake manifold vacuum, then the other port hooked up to the vacuum canister on the distributor...
Yup, that was the C.A.P. (Cleaner Air Package) that started in 1966. It changed how the vacuum advance worked and had different (read retarded) timing specs.