I think 2.5 is same bore as original, if I am not mistaken, I am more worried about the overal shape, because if its from MY06+ the shape of the piping will be different I am afraid
I have a Ninja 100 cell sports cat I bought from Scoobyworld a few years ago to put on my 2004 UK WRX SL (blobeye). Was never fitted so still brand new. Was £299 plus shipping new. If interested send me a PM with an offer).
its from his bugeye wagon he just sold i would say
Will a 100 cell sports cat pass nct charles?
Was told at the time it would pass... and still says it should pass UK MOT with it on the Scoobyworld website.
As never fitted it myself don't know for sure and can only go by what Scoobyworld says.