The "UXC 430" plate is correct for a car registered in California from 1967.
The ### XXX plate series was letter driven, not number driven, so a 6## XXX plate could be from a car registered from 1969 through mid-1980. Trucks, including ElCaminos, had a different series that also was revised in 1981 when the additional 7th character was adopted.
As far as I know, California records for titles and plates only go back to 1981. Prior to that, they were archived on microfiche only when a car was destroyed at a salvage yard.
