Shake rattle and roll

If this is a balance issue which is the most likely scenario. What would be my next step here. I have all the correct ingredients. The torque converter is a nuetral balance that I had built by a reputable shop that was recommended to me by the owner of a transmission shop I know. The dampner is off of a 96' 360 motor and I have tried an aftermarket with multiple removeable weights as well with the same symptoms. The keyway for the balancer is in good shape and the flex plate is the factory one with a weight that was installed on on the motor when I pulled it, and only goes on one way. Rusty Rat Rod had suggested getting it balanced professionally, but I dont understand why this would be necessary. There are tons of guys who swap magnum 360's and none of them have ever mentioned having to balance the engine afterwards. Is there a chance that the nuetral balance converter could be having issues and throwing off the balance? Im not sure as to what step to take next.