JDM ITR 4-1
JDM DC Sports
Spoon
Toda
JDM Mugen
etc...

All of these headers use a 2.5 collector which will all require similar modification to make them work. You can use a 2.5 >> 2 collector pipe and mate it up to the stock cat but you will most likely have to take some length out of the exhaust piping because i believe the JDM ITR is longer than the stock header.

None of the headers will bolt directly up to the stock cat i would reccommend getting an aftermarket 2.5 Cat or testpipe for the best fitment.