1968 production was at Wixom (Y) and Los Angeles (J). This view sorts 1968 cars by engine, then sorted by last six of the VIN without regard to assembly plant.
Although no examples of Z-code (390) 1968 Thunderbirds are known to exist, documents indicate that at least 2 were produced. These cars are not in the Registry but this page will update if and when they are identified.