so i work at advanced auto parts well a custumercame in and bought a glsspack to put in place of his catalytic converter on his 84 z28 with a hooker catback well i dont know what this would sound like, i dont think it would make a diference with the sound, but has any one here done that before?

It will be louder and more free flowing than with a cat. Not quite as loud as a test pipe or eliminating the cat but its the same idea basically. If it were me and I was taking the cat out mind as well replace it with a free flow empty resonator pipe or strait test pipe.