Boy would I like to get one of these, and with drum brakes, too! The true pre-cursor to the whole small wheel in the back and big wheel up front movement, and for an easy hundy! I am really tempted but I imagine the frame is probably too small for me. It, just looks small. In fact if you stare at it long enough what it looks like is simply a BMX frame with bigger wheels.
So, 24 inch wheel in the back and 26 inch wheel in the front makes this bike 64er? Other people opt to call the 69er a 96er but I prefer looking at the bike from front to rear rather than rear to front. But if you did take the other approach I guess this means you would have a 46er. Sounds better.
According to the vintage Cannondale brochure that I have from 1985 (pdf):