Fluctuating neg. to ground on ignition coil

I'd suspect that the vacuum reading changes are from the engine's erratic firing. The actual readings look pretty good. OK on the no visible fuel drops in the carb.

What is your idle ignition timing? Do you have a timing gun? I am not a big fan of maximizing the idle speed with ignition timing... you can end up with far too much idle timing and not know it.

I like the suggestion on the worn distributor bushings.