First up would be to check the diagnostic codes from the ecu surely?
Obviously if the motors no longer in the car thatll be hard!
If youve got no idea of the history of the motor id also be inclined to check the cams are correctly timed ( inside the cam covers) as its quite easy for these to be out if done carelessly.
Can only otherwise second what others have said.
regarding the mount; How was it "modified"? If its one of mine it shouldnt need any additional stuff doing to it.

Got a photo at all?