Johnny Downs?

Johnny Downs is credited as singing with Joan Leslie, "Somebody loves Me;" however, I don't believe it is him. Johnny Downs I believe is the tall Dennis Day looking fellow who is dancing to the Tin Pan Alley scene which is the lead to swanee. The actor who plays the ukelele while whistling and singing with Joan Leslie looks much older than what Johnny Downs would have been? If somebody knows the details please verify my theory or refute it. By the way,
Oscar Levant's body with Robert Alda's head was superimposed while playing the piano except for some close up scenes.