Has an AFL game ever ended 66-20?
Exactly once. On May 20, 1899, Essendon beat St Kilda 66-20, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 66-20 in league history.
That makes 66-20 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 67-20 has happened never and 66-21 has happened never.