I like the header and muffler but more for the sound. They don't do anything really for performance. They may give 5 to 10 hp gain but nothing you can feel in the seat of the pants.
I got the muffler from quick o muffler on Magnolia down by the fair grounds. 85 bucks and 45 minutes I was out the door.
The 2.7 just doesn't respond to well to performance mods.