RE: Header comment on the 6.1L engine
From what I have read, it will pass tailpipe test and ecu test, but if the tech were to visually see it, he could fail it because it isn't smog legal. Then you would have to put the old one back on and goto a CA smog station for inspection.
Also if the police see it, that is a ticket and you would have to take it off and put the other back on then take it in to get it signed off.