Mid length headers will also move the cats. Because you're in California it's probably not wise to go down this road. Headers really should be tuned and then you can kiss any chance of having your car worked on if something goes wrong in the drivetrain.
2015 Mustang GT Premium Sold
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2.3 Whipple, fully built motor with all the bolt-ons 718 rwhp/735 rwtq Sold