Need help with vibration

You have an imbalance in the engine. 360 have a counterweighted harmonic balancer as well as a counterweighted torque converter. The amount of counterweighted torque converter depends upon wether your engine is a Magnum 360 or a Commando 360. the weights are easy to weld on while in the car. There is a diagram of how much and where they go in the MP book.