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If you haven't already, it's worth a try running CA Plates through the Old Newspaper Websites as CA car ads back in the day required Vehicle Plate #'s be included in the ads.
Only a small percentage of papers have been scanned so it's a long shot but you may get lucky.
I no longer have a subscription but was surprised how well these websites work when I did finding tons of cool old ads including some for Member cars w/ CA Plate searches also lots more interesting stuff too.
Others here w/ Newspaper site access may be able to help or give one of the free trials a whirl and good luck!
~ Pete
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