I think all SS cars became Dana equipped by default in 1966, although it wouldn't surprise me to see an 8-3/4 in one somewhere along the way... I've got the book on the Super Stock history, I'll have to dig it out and see what it says.
Not sure if I am on the right page here. The 68' Hemi Darts with the automatic transmision came with the 8 3/4, but could be ordered with the Dana 60 as an option. All the 4-speeds had the Dana 60.