Has a World Cup game ever ended 7-3?
Exactly once. On June 8, 1958, France beat Paraguay 7-3, and no World Cup game before or since has ended that way. When it happened it was a scorigami, the first 7-3 in league history.
That makes 7-3 the 26th most common final score out of 34 that have ever occurred in World Cup. One point away, 8-3 has happened 1 times and 7-4 has happened never.