A-904 History Please

Hey folks I spent this last Saturday cleaning up a 904 tranny and was wondering what the difference was between the years? Mainly my 1967 and up. The 904 I cleaned up (72 Duster) looks a little different than the one in my car, is it just the casting or something else. Anyone know of a good book to rebuild these with, or information on the subject. Google aint all that you know!

John B.