You could cut the muffler off and weld on a 3" Classic Chamber unit. If you want real loud turn the louvers where they will not scoop the air.
I replaced my 24" ( which is average length ) with a 28". I cut a cut a couple of inches of pipe from the front and rear to keep the tail piece in about the same place.
Oh yea, I turned the louvers to scoop the air to quiet it down. Worked great.
Loud rumble at idle. Quiet enough at hiway speed to easily talk with my passenger.
You will have to get the side pipe recoated or spray them with high temp silver rattle can paint.
Classic Chambered Exhaust Inc. - Cobra
Dwight