There are several interesting things about the plates besides showing the car as Long Beach assembled.
Paint number is a lacquer code, which it should be for either a Long Beach or a Portland (or for that matter, a Jackson MI) assembled car. Bodies were shipped in "white" welded panels with doors and trunk attached, but not painted. The assembly plants were not set up to do the high-temp Enamel of Willow Run.
The car also appears to be one of the original "sampler" cars...the first production cars going out to dealers and distributors. AG4 was used on cars since the start of production (March 1950) until around June 15th 1950. Cars with AG4 did not have electric clock or electric wipers.
The serial numbers (body and car) suggest that K-F assigned the numbers when the bodies were shipped out rather than on the line (in other words, the numbers ran sequentially for Michigan, Oregon and California built cars...the Prefix identified assembly point for warranty and other purposes).
The latest information I have on Long Beach production shows that by 10/31/50, 1,104 Deluxe 4 doors were assembled out there. The plant operated in spurts through March 1951 when the 5-year lease ran out and K-F vacated the facility so Douglas aircraft could expand military plane production.