American Motors: 74 Javelin Vibration, torque convertor, vibration problem

Question
QUESTION: HI, I have a 1974 Javelin, with a 1000 miles on the drivetrain, it has a rebuilt 403 engine and rebuilt 727  transmission. I have a vibration that comes in at 50 MPH (no Tach so I don't know the RPM). The vibration can also be reproduced with the car in PARK when the revs are high enough. I have disconnected all the belts to eliminate the power steering pump, Alternator and water Pump as possible causes. It is a pulsating harmonic vibration, not a steady vibration, that I feel coming up thru the seat area.It feels like a classic drive shaft balance problem and had the drives balanced,they took a weight off. Next I change the Harmonic Balancer with a new one, problem still there. Took my converter off and brought it to a converter shop and had it checked, this is a rebuilt one I got the same time the transmission was rebuilt. They said it was seriously out of balance.So I got a new one. I still have this Vibration problem. Any ideas of where I could look to solve this problem?
Thanks Steve

ANSWER: If you can feel the vibration with the car in Park, it can only be the engine or transmission.
You say you have a "403", Being that AMC nevcr made an engine this size, I am assuming that it is a "401". This engine uses a different harmonic balacer that other AMC engines. Are you sure you have the correct harmonic balancer? I have seen this happen when a balancer from a 304/360 is installed on a 401.

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QUESTION: Hi

Sorry I had a typo mistake on the engine size, my engine is a 304.The Harmonic Balancer I installed was a "powerforce damper" with the separate weight of each of the engine sizes and the correct balance weight is installed for my 304.
Thanks Steve

Answer
When the engine was rebuilt, were any of the connecting rods, pistons or crankshaft replaced?
You could disconnect the torque convertor and push it back into the transmission as far as it will go. Start the engine as see if you still experience the vibration. If you do, I would suspect something internally is out of balance. If the vibration goes away with the torque convertor disconnected, you have a problem in the transmission or convertor.