318 vacuum advance

Well double check the pickup wires. I don't know how you made the connection to the MSD. I've done it a few different ways. Definately easy to get them switched up since its not a plug in.

I don't think you'll have to mess with the spring tension. At least we dont have information pointing that way yet.

From what you describe the vac port connection seems correct. We can check that.
I have the factory electronic ignition connectors from the msd to the distributor which already came with the connector