random tech and stromung are the only "bolt-on" cats out there. i would save the money and do the cat and header together. if u get the random tech one, u probably won't throw a CEL, where the stromung is more likely to b/c it is only 1 cat. this is the easier, more expensive way.
if u do "frankenstein" it, u need a 2.25" inlet and outlet diameter and 2 cats to not throw a CEL. then u have to have the shop bend the pipes in the right way and add flanges so it will bolt up to the stock header. this is the harder, cheaper way.
i did the "bolt-on" way, although more expensive. the sound is sick, especially if u have a catback on the car. mine is the stromung single tip and definitely recommend it if u don't have a CBE yet.