Nothing proven. Most of that stuff takes a lot of man hours and metalworking labor. You get into the whole project for more than it would have just cost to buy a set of pipes tailored to what you want. Someone was saying they did it for stealth with a high hp motor. That seems like an awful lot of work and money just to try and trick someone. When in the long run, if you still get beat with the gutted pipes, then where does that leave you?