Actually, not to be too big of a butt or anything, but you CAN remove the 1st set of cats, install the headers, relocate the rear 02 sensors to BEHIND the 2nd set of cats, and it WILL clean the exhaust enough to keep it within emissions specifications. This HAS been done, this is PROVEN, not supposition. So in that regard, you CAN still be within emissions specs, both visually AND sniffery (is that a word??) AND OBII, with the headers.

However, you wouldn't have the fancy schmancy CARB approved sticker, so in California, odds are, they'd still fail you since you can't prove the headers are CARB approved (they're not).