The one broken in half is definitely an imitation pearl. See the peeled off coating?
If the pearls are all the same as that one, then they are imitation. I have owned fake pearls that had a bit of variation in their shape throughout the strand.
It would be unusual to finish imitation strands with gimp and 14K clasps, though I suppose it could be done. Silver was not unusual for nice imitations. Gold used to be much less expensive than it is now.
There were no cultured round freshwater pearls in the 1960s. And clearly they are not south sea pearls.
That leaves imitation or akoyas for your pearls. But 8+mm akoyas would have been quite expensive. And many akoya strands in the 1960s would have been graduated strands. This makes me lean toward imitations. (Also the fact that they are very similar in color, have relatively low luster and have no overtones.)
Here is a test you could do if you have any pearls that you know to be real, or know to be fake:
Leave the strands to be compared in the same location for half an hour or so, so that they are exposed to the same ambient temperature. Then place one strand against your lips. Repeat with the pearls you know to be real or fake. Real pearls are cooler than fake glass pearls.
There is another test that will settle the question but it would be destructive to one pearl if it is a fake. It won't harm the pearl if it's real. Acetone (or nail polish remover) dissolves and removes imitation pearl coatings from the glass bead underneath. A wipe with acetone won't harm real pearls-- just don't soak them in acetone for a prolonged time.