Has a FIBA World Cup game ever ended 81-53?
Exactly once. On July 9, 1986, Cuba beat Angola 81-53, and no FIBA World Cup game before or since has ended that way. When it happened it was a scorigami, the first 81-53 in league history.
That makes 81-53 the 240th most common final score out of 863 that have ever occurred in FIBA World Cup. One point away, 82-53 has happened never and 81-54 has happened never.