Vintage Vehicle Registration in California

I have a friend who purchased a 1935 car and wants to restore/modify it. What is the best way to register the car with the Cali DMV? It was purchased in Oregon and there is no current registration - only a bill of sale. Should the process start before any restoration begins? Is there any issues with doing it after the restoration is completed? This will be a complete restoration with new drivetrain and chasis.

I have some idea what the best procedure is but, I'm hoping some here may have gone through a simular situation and can advise of any pitfalls to watch for.