318 Poly Vibration

If you mean changing an old plug to a new plug, then running engine, then changing another, etc, no I haven't.

I have changed the plugs multiple times during this, just recently on Tuesday.

I just tinkered with it a little more, nothing major, very small adjustments to timing and idle. Ran extremely well, nothing new there, but that vibration.

Anyone thinking spun bearing or something else major?
I'm not sure how that manifests itself, or if that would stay constant at any rpm for an extended period of time.