i was just looking at 04 and 05 bins in tiny tuner, i see no cat test listed.

your best to get a cat. they fit in place of the mid pipe in the down pipe of sd headers just fine. i got a 3 inch hi flow, your conna want something closer to stock cell count to keep the pcm happy.

ive seen a guy here, he cut off and opened up the in and lets of the stock cat and welded the 3 inch pipes to it. iirc hes in ca and needed the factory cat.

in your case its likely the best route to go due to the pcm using the rear o2 sensor.