You ordered an exhaust without verifying it will fit first? Good news for you is dumps fit fine seeing as the only thing specific about the IRS catback is the tailpipes which are not present on dumps.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.