If you are in CA, and If you follow all the state ref's guidelines like asiandood said, you should be fine, hence like he stated earlier: Engine must be same year or newer than the car; must have correct ODB setup, pass sniffer test, pass visuals (wiring, etc) you should be fine. Usually "MOST" people when they do something like a b16 or b18 swap into a civic, they leave the OEM airbox, header, and sometimes exhaust to help visual passing. Sometimes they can get away with the CARB'd intake for the b16/b18 and header for the b16/b18. But the issue with that, is that the CARB #'s for those intake/header is technically classified legal for the del sol or integra, and not for the civic, so it depends on the REF sometimes too. If you're paranoid, just go with the OEM intake/airbox and header. For GSR swaps, people like to use the GSR intake, and Civic airbox.

As far as turbo-D CARB issues, I believe 2 of the name brands that have 50 state CARB legal kits are Greddy (w/o intercooler) and Edelbrock (Their kit includes an intercooler with their legal kit), just to name 2.

As far as JDM engines passing smog, that depends on who you get. I've "HEARD" that as long as you have the US Spec ODB wiring/ECU for that year car that is eqivalant to the donating engine/car, you can pass. Asiandood, please confirm this.