I just took a set off a 65, and without looking, I remember Yankee 77, or something similar, in the top of the casting. I don't know for sure that they're factory originals, but they look the same as all the others I've seen.
Yes, Yankee 77's are the correct ones. I believe the options were to have 2 on the corners only, 3 in the middle only, or 5 (3 in the middle and 2 on the corners).