I might have found the applicable section at the bottom of this page:
V C Section 4456 Use and Display of Report of Sale Forms
Excerpt:
(c) A vehicle displaying a copy of the report of sale may be operated without license plates or registration card until either of the following, whichever occurs first:
(1) The license plates and registration card are received by the purchaser.
(2) A six-month period, commencing with the date of sale of the vehicle, has expired.