Has an AFL game ever ended 70-20?
Exactly once. On July 6, 1901, Sydney beat Carlton 70-20, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 70-20 in league history.
That makes 70-20 the 3884th most common final score out of 6,649 that have ever occurred in AFL. One point away, 71-20 has happened never and 70-21 has happened never.