As long as CA doesn't change the laws you will be fine. My brother Scott had my old 92 F350 out there with a heavily modified 12V Cummins and I'm certain you could follow him every where he went by the trail of smoke. He did get some warnings but never got a check or fog test. If he stayed there any longer I'm sure it would have been game over. Now if you had a commercial truck, it would be a different story. I actually got into it with a state official because he was declaring that the emissions laws are to match the engine year and not the body model according to him. But in reality, which ever is newer is what the emissions have to be met to. For instance if I put a 1994 engine in a 2008, the emissions laws for 2008 need to be passed. Luckily in Iowa it isn't an issue but it could be down the road.