I had the flexplate problem that Don C alluded to. I don't know if my old thread will help you, but here is a link:
https://7173mustangs.com/threads/please-help-me-diagnose-vibration-1966-289-4v-solved.41589/
Unless your engine was rebuilt or replaced with a later year 50 oz balance, and you have the same issue as me with an improperly installed 50oz flexplate, then swapping the plate for a 28oz is the only fix.
Good news though, you don't have to pull the transmission. With the coolant lines...
Anyone heading to Columbus for this event should plan on spending Monday in the area. The path of the total eclipse is just a few miles down the road.
As anyone that has ever seen complete totality can attest, it is worth the effort to experience.
Alternatively, if you don't want to re-stab the distributor, you can always pull the coil wire and just use the starter to circulate the oil. If you are worried about abusing the starter pull the spark plugs first.
I'm a VR1 fan as well.