Your comments about modern air-to-air missiles may be correct, but in 1968, the beyond-visual-range (BVR) engagement was more of a bomber general's fantasy than a reality. Kill probability of the AIM-7 Sparrow missile in those days was less than 10% [1].
Pilots' accounts of air combat in Vietnam routinely mention the firing of a salvo of missiles --rather than just one-- when a firing solution presented itself, due to the notorious unreliability of missiles.
The specific aircraft I was referring to, the F4 Phantom II, first flew in 1958 and was introduced to service in 1960. The missiles that the designers had in mind were the Sidewinder and the marketing promises of the Sparrow.
And also, the sparrow had a decent hit probability -- that is, unless the target aircraft released chaff, in which case it was very unlikely to hit.
Pilots' accounts of air combat in Vietnam routinely mention the firing of a salvo of missiles --rather than just one-- when a firing solution presented itself, due to the notorious unreliability of missiles.
[1] https://en.wikipedia.org/wiki/AIM-7_Sparrow