I started working is Service Station, AKA Gas stations in 1961 and learn most of what I learn to work on cars back then.
All the Chevy cars that came in for tune ups that i remember had manifold vacuum for the vacuum advances, you had to disconnect them and cap off the port to set the initial timing is what I remembering now Not so on the Fords and Mopars
I do remember also that GM swap to ported vacuum some time after 1961