Technically aftermarket headers are not street legal in Commiefornia but if nobody looks at them, they don't throw a CEL, and you pass the sniff test you
may pass smog inspection. Your primary O2 sensors need to be pre-cat, and your secondary sensors need to be post-cat. With a good set of cats your car should run clean with no CEL. I would probably save the headers for a dedicated track car and sleep better knowing that the KGB wouldn't show up in the middle of the night and impound my daily driver.
