Look at the modifications in my sig if you want to stay NA and still pass smog.
I have the front plog as long as other modifications for an NA and the car is much more spirited than its stock form. My brother had the plog when he was top swapped. Headers are not carb legal in California other than I believe the TOG's.
I am in California in the same location as you and a turbo is not legal. You would want to go the top swap route. You can find the newer style w-bodies at the salvage yard for parts. Check them out as you can on occasion find a supercharged engine. This is what my brother did when he top swapped his 03 that passes smog. It was nice to drive before he sold it. I thought about it but never did and probably won't. Mine is just a daily driver these days.
Here is the link to look at the local salvage yards
Salvage Yards Near You | LKQ Pick Your Part