69 Barracuda Clutch Shake Help Needed.

Sounds like a clutch release chatter interacting with the natural resonant frequency of the spring and axle wrap. That is always there unless some positive control is added to stop it.

BTW, what DO you have for motor and trans mounts? They are all part of the drivetrain wrap up.

I had the same type of thing in a plain old /6 early Dart. A different new clutch solved it. Nothing could clearly be seen wrong on the other one, but it chattered just the same. Could be a lot of things in the clutch area.