Amazingly, the production directed by Franco Zeffirelli marked the first time Ms. Callas and Mr. Gobbi together performed "Tosca" before an audience. (Alas, Mr. di Stefano is absent.) But the voices are a decade older.
Time was when you could give audiences a thrill simply by casting young actors in the title roles, but ever since FrancoZeffirelli filmed the sorrowful tale of the star-crossed lovers in 1968, that expedient has come to be taken for granted.