Here is the parking brake section of the State of CA V.C. It does not say anything about how many wheel have to have them. Back in the 50's-60's used a d-shaft e-brake which is basically on one wheel because of the diff. If you have a non-selectable locker, spool or welded rear diff both wheels are locked when the e-brake is applied.
26451. The parking brake system of every motor vehicle shall comply
with the following requirements:
(a) The parking brake shall be adequate to hold the vehicle or combination of vehicles stationary on any grade on which it is operated under all conditions of loading on a surface free from snow,ice or loose material. In any event the parking brake shall be capable of locking the braked wheels to the limit of traction.
(b) The parking brake shall be applied either by the driver's muscular efforts, by spring action, or by other energy which is isolated and used exclusively for the operation of the parking brake or the combination parking brake and emergency stopping system.
(c) The parking brake shall be held in the applied position solely by mechanical means.
Here is a link to the California V.C. where you can read about lighting/refelector requirements.
Remember lights or refelectors are required on the front and back sides of the vehicle.
http://www.leginfo.ca.gov/.html/veh_table_of_contents.html
