To register it in CA you have to take it to a State Smog Referree. He will do a visual inspection and make sure all the correct smog equipment is there, and make sure the engine looks like it belongs in the car. Then he'll put it on the rollers and sniff test it...if you pass, you get a nifty BAR association sticker for your engine bay, saying the smog is legal. Then you can take it to any smog station and have it smogged, but it must be reffed first.