I woudln't bother, there is a free flowing cat already fitted to the FRP. It'll be more hassle getting it through MOT's without it, it's a nightmare getting them through with them!
Ive de-catted mine, the lambda sensor should be before the cat so it wont effect how the car runs and wont bring the light on, pops alot more and if you rev it and left off the throttle as hits red line itll pop a flame oh plus 10-15 brake