Possible Clues:

• Lettter rearrangements
• Words made from re-arranging other words
• Lionel and O'Neill
• Angered and enraged, e.g.
• Matter of letters from a horse to the sheep?
• Ones for the answers to 1-, 25-, 37- and 50-Across are hidden in their clues
• For the actors, or cast, 'Sister Ada' is a disaster
• Lemon and melon, e.g.
• Popular word game
• Clue to how 'rate mortgage' is adjustable herein