I have the same car and i purchased the slp stainless steel dual exhaust.It fits under the rear bumber without the cutout the borla needs to have cutouts. the slp sounds nice and it produce more horsepower. aftermarket parts go to GAUpgrade.com,PFYC.com ok.
Grand Am GT's DO NOT HAVE DUAL EXHAUST! Infact the muffler is just a single inlet and quad outlet look for your self. If you want a good exhaust try that pfyc site for borlan exhaust or customize a exhaust setup your self. DoctorSpeed also carries grand am exhausts. Both sites have only CAT BACK systems which work nice.