318 Poly Vibration

Yes, I ran it at least twice with the belts off.
I went as far as running it with only one belt on, then the other. I don't know why or what I thought I would find.

I'm thinking the consensus is the issue is not within the engine itself.

I am unable to get a new trans mount, it's just not available for a 64 b-body, and only rubber engine mounts.

I have my old motor mounts and damper.
Should I swap those in and see what happens?

Thank you to all who have stuck with me on this, I feel we're closing in on it.