I would like to see the plugs (in order) 1357-2468.
And raise the idle 100-150 rpms.
This is what I start with.
Then make sure all 8 are firing would be next.
Then I’d be all over that ignition timing (initial and total both)
You can screw with vacuum advance some other time.
It’s possible the really low idle and a mild cam could make a “shake” and cause a jumpy vacuum reading.
