Resonating vibration

Great info and exactly what I was looking for. Any recommendations on a flex plate and balancer, this isn't a race or show car, I plan on driving it.
Can't make any recommendations until you answer the previous questions-
Is this a stock 5.9 bottom end, or a stroker, and was it rebalanced during a previous rebuild?
And, if it was rebalanced, to what specs? Neutral balance or external balance?