I HAVE A 94 MUSTANG GT AND RAN INTO THE SAME PROBLEMS. I ENDED UP GOING TO A SHOP, AND THE INSTALLER TALKED ME INTO TWO SOUNDSTREAM SPL 15 WITH A SOUNDSTREAM RUBICON 702. hE MOUNTED THE SPEAKERS IN THE BOX FACING TOWARDS THE TOP OF THE TRUNK, AND SLID THE BOX IN THROUGH THE FLIP DOWN SEATS, SO I FEEL YOU SHOULD HAVE NO PROBLEM FITTING TWELVES IN. MAKE YOUR BOX LONG AND WIDE RATHER THAN TALL, BUT JUST MAKE SURE THAT YOU CAN FIT IT THROUGH THE OPENING GOING INTO THE TRUNK. ALSO, BEFORE YOU SCRAP THE MACH460 SYSTEM TRY REPLACING YOUR HEAD UNIT, IF YOU HAVEN'T ALREADY. THE SAME INSTALLER USED SOME OEM ADAPTERS TO MAKE MY ALPINE CD PLAYER COMPATIBLE WITH THE SYSTEM, AND THE DIFFERENCE BETWEEN THE STOCK HEAD UNIT AND THE ALPINE WAS UNBELIEVABLE. COULDN'T BELIEVE IT WAS THE SAME SYSTEM. MY SYSTEM HIT 148 SPL AT A LOCAL COMPETITION, WHICH TO ME IS PRETTY LOUD, AND NEVER HAVE I FELT THE MACH SYSTEM WAS HOLDING ME BACK. WISH YOU LUCK AND HOPE THIS HELPS.