I have the same question that buzzin has. In my experiance, I never use a used motor without tearing it down and lapping the valves, ball honeing and rings and bearings. It sounds like you have a spun main bearing. If the donor car has been hit hard in the front or the motor was dropped, it is really easy to bend the crank snout. This would cause the wobble you mentioned.Just my 2 cents.
