74 dart vibration problem.

So I bought this 74 Dart. Rattled like crazy on the drive home. I had the engine rebuilt, front end rebuilt, new shocks, New engine mounts and trans mount, alignment, new carb and this STILL vibrates with acceleration!!!! This is driving me nuts! I take it out at about 50-60 mph and then throw it in neutral and NO VIBRATION so it isn't the driveshaft. Has a 318/2 brl carb with the stock auto trans.

The engine rebuilder put a "motor home cam shaft" in it for better perfromance, hope thats not the problem. I can sit in park and accelerate and I get vibration. The motor is tuned and timed perfectly. What is my next step?

Do you guys think it could be the converter of flex plate?