Brian
Given the number has a C suffix, it would be 1965, which would make it potentially on a Flavia Sport. (I think only one (production) Fulvia Sport was made in 1965). If the Fulvia Sport was registered with a cherished number, then I would suggest that you enquire if the person can remember what number was assigned to his Fulvia Sport after the cherished number was removed.
Regards - Roddy