As far as I recall all the Ford 221-260-289-302-351W were externally balanced. The 302 used a 28 oz imbalance up until about 81 at which time it went to a 50 oz imbalance.

It sounds like you put the wrong balancer on as you now have a worse vibration.

First, I would put the proper/original balancer on the engine. Check the size of the counter weight on the balancer you took off against the new balancer,they should be the same size. If not get the right one.

Next figure out what RPM your running at 80 MPH. Put the car in park and rev the engine to that RPM. If you have a vibration, it is a problem in the engine/torquer converter/flywheel-clutch.

If you don't have a vibration, it's either in the rest of the drive train, tires and wheels, or even resonance form the exhaust.