[dscott]

Ken, The only thing you can do for the header is cut out the liner and reglass it or put a small metal plate over the hole indented for clearance. The vibration is typically harmonics from the engine. Some vibration is normal and since the sidepipes are solid mounted to the frame you will feel more than normal. If you isolate the rear mounting on the sidepipes that will eliminate most of the vibration feel. If the vibration is harsh then the engine may be out of balance. Sometimes the clutch will cause a vibration and the fix is to rotate the clutch to a different position.
Don