[Halz]

Section 4161 of Division 3 - Registration of Vehicles and Certificates of Title deals with putting a new engine/motor in a vehicle.. It reads:

Engine or Motor Change: Distinguishing Vehicle Identification
Number
4161. (a) Whenever a motor vehicle engine or motor is installed, except
temporarily, in a motor vehicle which is identified on the ownership and
registration certificates by motor or engine number or by both the motor and
frame numbers and subject to registration under this code, the owner of the
motor vehicle shall, within 10 days thereafter, give notice to the department
upon a form furnished by it containing a description of the motor vehicle
engine or motor installed, including any identifying number thereon and the
date of the installation. The owner of the motor vehicle shall also submit to
the department with the notice the certificate of ownership and registration
card covering the motor vehicle in which the motor vehicle engine or motor
is installed and evidence of ownership covering the new or used motor vehicle
engine or motor installed and such other documents as may be required by
the department.
(b) Upon receipt of motor vehicle engine or motor change notification and
other required documents, the department shall assign a distinguishing
vehicle identification number to motor vehicles, other than motorcycles or
motor-driven cycles registered under a motor number or motor and frame
numbers. When the distinguishing vehicle identification number is placed on
the vehicle as authorized, the vehicle shall thereafter be identified by the
distinguishing identification number assigned.
(c) Notwithstanding any other provision of this section or any other
provision of law, the department shall not register a case for any motorcycle
of the push-rod type with nonjournal rods and four-stroke engines,
manufactured in the United States, without proof of the destruction of the
case being replaced. A determination verifying proof of destruction shall be
made by the Department of the California Highway Patrol.
Amended Ch. 755, Stats. 1982. Effective January 1, 1983.

It sounds pretty open-ended..