I'm helping my friend do a few things to his 00 camry. I'm re-doing my suspension and giving him my old set-up, and a few other things. One thing I noticed is that he doesn't have a Cali model and I do. What I'm concerned with is the header. I have a cat after the 4 tubes meet, his is just one pipe. Could they be swapped with out messing up the ECU or O2 sensor? Also how would gas mi/ pewrformance be affected on both? Thanks.