If the goal is better sound why not just change out the muffler, resonator and/or add an X pipe? Headers will change the sound some but not near as much as downstream exhaust work.

Installing headers even on what they were designed to fit is seldom problem free. Even if your goal is to improve performance headers would be way down the list of least spent for greatest gain.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas