I can tell you that the headers modification does NOT rectify the smell. The headers will replace the front cats, but there is a set of rear cats as well. I have had my headers on now for about 2 weeks and tried driving with the rear window down, in hopes the smell would have gone away with this mod.....nope!
One of the members here "Jed" replaced his cats and the smell went away. Here is what he bought:
Got a Walker cat. You can find them at just about any auto parts store, but they may have to order it for you.
That seems to be the fix, or an entire AM exhaust.