Vanbuski -
I'll be registering a 1981 Aurora Cobra next week, so I researched this. If you want to register your existing car/engine block, the California Bureau of Automotive Repair has a "Referee" service, with whom you'll need to make an appointment. The appointment scheduling number is 800-662-7733. You'll need to bring any existing registration, topped up
oil and coolant, working gas cap, $35 fee plus $8.25 for a certificate.
They'll schedule you at a location of your choosing, and the review/exam/test takes about 50 minutes.
Good luck