Pick your headers for quality. They don't have too much effect on sound (other than making things louder)
A big part of the modern mustang sound is the 4v engine, cam profile, the wide VVT spread, and the exhaust crossover. If you want that raspy rev and cackle you will need to go to an x pipe. You can "sort of" get it out of the y pipe, but it will never be what you're looking for. To mimic the sound you will want to run a lightning style exhaust, the shorter the better. You will also need cams to get the RPM. Run the Corsa extreme with resonator delete and you will at least get some jackhammer noise, but it won't have that wound out race car sound you're looking for.