No problem. Just helping out from previous personal experience with various exhausts. I've had my fair share, this will be my 9th Mustang, and I've also owned 5 Camaro's lol.
Borla Stingers are not a race sound. I've had them on my 02 and my 2006. They are very deep. SLP's are much much louder and more race car like in comparison. If he don't like them then he won't like Borla if he wants a raspy race car like sound.
They might, but sometimes being that it's no longer your car, they may not release that information even if they still do have access to it. It never hurts to try though.