Notice in the 1969 catalogues that the six strings have headstocks that diverge, yet just about all the other later six stringers in the catalogues have that convergent type.
Other than my guitar, my abiding memory of Yams was that they had the divergent headstocks then the 'V' shape.
Wow, this is quite exciting when you're this obsessed.
I can find any amount of information on my Martin, but frankly, I thought that this Yamaha information was lost forever. Happily, I was wrong