Vibration in driveline or motor/tranny mount ?
Is that the original motor? Are you sure?
My '65 Barracuda had a bad vibration. I balanced the tires, replaced the ball and trunion...everything.
What was it? Turns out the newer engine (1969) mated to the 1965 transmission has a problem. The snout on the torque converter is smaller than the hole in the back of the motor. The snout needs to be perfectly centered or you'll get mad vibration! I assumed whoever put the motor in did this, but when I changed the motor I found out otherwise!
You have to add a small sleeve to take up the extra space. It's well documented in some books and other places. You can buy the sleeves or have one made, I had one made. The specs came from a book and are accurate. This solved my problem.