Help! Engine Vibration

Red,
Yes the pistons were replaced as well as 2 of the rods. I don't know about the prevois balancing. I don't recall any balance plugs on the crank so I'm assuming it was stock.
The motor was previously hooked up to a 74 duster with a manual 4 speed tranny. My demon has a 904 auto with the original torque converter/ flex plate.