Possible Clues:

• At last, a supporter of the steering mechanism?
• Once and for all
• North America circumnavigated by horse in the end
• Adverb synonymous with the phrase formed by the first words of 17-, 27-, 47-, and 63-Across
• Fine and altogether dandy ultimately — that's how this clue comes across
• Practically excellent friend for ever
• In the end
• Endlessly excellent friend at last
• Exclamation upon reaching a customer service representative, maybe
• Female friend hanging around home at the end of the day