Possible Clues:

• 1550, to a 60 Down
• L x XXXI
• Super Bowl ___ (game that will be played in the year 3516, we assume)
• 1550, on some hypothetical cornerstone
• 1550, in Roman numerals
• Year that Michelangelo's 'The Crucifixion of St. Peter' was completed
• Mid-16th-century date
• Roman 1550
• Year in the reign of Edward VI