If you do the GSR swap, you can use your LS header/cat/b-pipe and everything will be fine. If you use a GSR header, you must use the GSR cat and b-pipe.
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2015 Ford Mustang GT Fastback - Ingot Silver - 6M - Performance Package - Gibson Catback, JLT CAI, FR 47lb injectors, BAMA E85 tune, Eibach Sportline, BMR wheel hop kit, UPR oil separator, Steeda shifter bushing/bracket
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