Catalyic question regarding smog

[niss]

Well, its time for smog (July). I was wondering if I could save some wrench time on making my car pass smog by just getting a high flow cat. I could just replace the header with the stock pre-cat, but if this could pass, i'd prefer to do that. Currently, my mods are I/E/H, jwt ecu/cams and pulley. Also, if I do get one, would a 3 inch cat affect performance? any info would be greatly appreciated. thanks in advance!
p.s. I live in California.