You wont see much gain with long tubes on our 6's. If you're looking for power, I'd suggest putting the $$$ somewhere else.
It may sound a little better, but it will never sound like a v8 with headers.
And as mentioned, if you retain cats (which you should), you'll have to figure out how to get them in.
FWIW, I'm using the Mac lt's; they were easy to install on the engine, but getting a catted system beyond that was a bit of a challenge, and ended up being a custom fab of high-flow cats. Completely emissions legal in my locale.

 

I don't have a video camera and have yet to take my car to the track. During the month of December I will do my damnedest to find a friend at work or in my Mustang Club with a video camera to film me in some footage of drivebys and idols. When I get it, I'll get you guys to tell me how to post it. Also, our Mustang Club is scheduled to go to Bradenton Motorsports Park Thursday evening, December 18th for "test and tune." I do everything possible to get my butt up there with the club that night and lay down some runs. I'll post the times with the exhaust video. Today I had to make some adustments to the exhaust pipes for clearances cause where the pipes go up over the rear axle the passenger side was banging on the support that has the bolts for the panhard rod. This is where the Stainless Works exhaust system shines, all the little pieces allow you to "fine tune" adjusting the location of where pipes run. Bangs are gone now - yeah! Also, got the new rear suspension components installed. Put on H&R rear lowering springs and Bilstein gas shocks. I got the sport version of the springs so it only lowers the rear 3/4 inch. The new ride is beautiful. Friday I'll put on the new front springs (lowers front only an inch, and I won't need camber plates) and new Bilstein struts. This job will take a few hours, that's ok, I love working on the car. Happy Thanksgiving to all. See ya soon, Jack.