Possible Clues:

• Motown group ... and what 17-, 25-, 37- and 46-Across comprise?
• 'I Can't Help Myself' Motown group ... and what's comprised by 18-, 24-, 39- and 52-Across' starting words?
• "I Can't Help Myself" Motown group ... and what's comprised by 18-, 24-, 39- and 52-Across' starting words?
• "I Can't Help Myself" group (or an alternate title for this puzzle)
• "I Can't Help Myself" singers (1965), and hint to puzzle theme found in beginnings of answers to starred clues
• Motown group