On most 760 machines the output shaft for the entire machine drive had no bushing where the shaft entered the flywheel.So after many hours of hi torque loads ,the pilot less shaft would flex and wear enough to let the output shaft dance within the flywheel. This was quite common on all perkins applications in combines including the Whites.This was the cause of vibration on my 760.The fix was to remove the shaft and flywheel and have them both refitted to each other,this time with a serviceable bushing.Not a fun job but it fixed the vibraion.