I'm on the same mission!
I'm not sure what you mean by fluted- is this what you mean?
Classic Chambered Exhaust Inc. - Products
I'm rebuilding my pipes over the next few months, I was going to mount one of the spiral insert units into my tailpipe, have it extend back into the end of the glasspack muffler section, I should be able to get 10-12" worth of spiral insert. I just asked on another post if anyone had done that;
Sidepipe horsepower loss?