3 different years, same transmission, which one should I use?

I'll assume these are all 904 automatic transmissions. What engine will you be using in the Cuda? If memory serves me correctly, the 66 tranny's require a different torque converter because of a slight difference in the either the pump or the snout of the tranny. I'd go with the latest year you have to get away from little annoyances like that and you can then use a standardized torque converter. I'm sure someone with more knowledge of the 66 tranny's will jump in here and give you the absolute correct answer. :)