Use the correct soft lines for the brake calipers you are using (IOW, if you have 2003 Mach 1 calipers, you need 2003 Mach 1 replacement soft lines). This will likely mean you need to use an adapter for the passenger side soft/hard line junction. Take your original lines into the parts store, figure out what thread they are by test fitting them with brake line fittings. That's exactly what I did, because I found that the common "brake line adapter" that a lot of Mustang parts outlets sell was NOT correct for my car.