Has a FIBA World Cup game ever ended 81-55?
Exactly once. On August 12, 1994, Croatia beat Greece 81-55, and no FIBA World Cup game before or since has ended that way. When it happened it was a scorigami, the first 81-55 in league history.
That makes 81-55 the 240th most common final score out of 863 that have ever occurred in FIBA World Cup. One point away, 82-55 has happened 1 times and 81-56 has happened never.