Be ready to buy a new catalytic converter!! The stock one will not fit the collector end. I did the same thing maybe a year ago, and I had to get rid of the CC. I had a Type-R exhaust system (2.25"), I know is not a good setup, I need to buy a new converter (maybe) and a 2.5" exhaust.

Also, buy the 2.5" gasket, you will need it also, same as the S2000 uses.

Good Luck