Possible Clues:

• Ailment also called 'the kissing disease'
• Precursor to 41-Across
• Single-track
• With 69-Across, what each set of letters in parentheses represents
• Like 45s
• Single
• The ''M'' in MSG
• "Kissing disease," for short
• "The kissing disease," for short
• Like pre-stereo sound