Bob:
In an effort to attempt to answer your question, I went through the Old Town build sheets for all the serial #'s in the 175000, 176000 and 177000 series. These 3000 craft seem to cover the 1966 year fairly well.
I found 18 9' dinghies having been produced, although the last two really didn't ship until the 1967 calendar year, and some of the first I have listed here were started in 1965, but were not shipped until 1966. The numbers I recorded are: 175084, 175164, 175253, 175271, 175292, 175354, 174393, 175455, 175881, 175890, 175943, 175985, 176087, 176134, 176157, 176781, 177242 and 177479.
During the same period, there were roughly 20 or 21 7-1/2' dinghies produced and about a dozen 11-1/2' dinghies. There were also about ten or twelve 10' fiberglass dinghies that I noticed.
My experience while checking the earlier OT records certainly confirms what Benson has already noted. The 9' length was the biggest seller in the first 100,000 units of production, followed by the 11-1/2' and then the 7-1/2'. At least that's my impression. After 1927 or so, the 7-1/2' length seemed to gain in popularity, and it's production numbers were running much closer to the others. Again, that was the picture created in my mind when flipping through the files.
Hope this helps to answer your question.