360 balance ?s

The keyway on the damper should, I believe, align with the #1 TDC. At that point, the timing marks should line up with TDC on the cover, as well. I may be incorrect on this.

The flexplate only goes one way that I've ever seen, thanks to offset crank bolts.

Does it vibrate at idle? Running at a certain speed? In neutral? In a certain gear? On jack stands?