There are no catless headers that bolt up with any factory positioned catback. I think GTPprix is saying he has the kooks mid length headers which have cats. Both Kooks mid length and SLP LT headers have cats and are the only 2 that are bolt on. To do what you want you would just buy a set of LT headers like Kooks, ARH, SWs or dynatechs and have a shop fab them up to the corsa catback.
320 rwhp/340 ft-lb
1/4 mile: 13.30 @ 105 mph