HELP 408 stroker bad vibration

You need to contact the engine builder and find out if your stroker was internally balanced or not. Then you can go from there as to which harmonic balancer and torque converter to use. A lot of these 4" stroker cranks are internally balanced and if you use an external balance damper and converter you will have problems like you describe. If you mix and match you will have shaking too. You need to use both damper and converter that is internal or external balance.