Compatibility

That is not a late sixties transmission. The trunnion on the end of the output shaft tells you that. I believe 1964 or 65 was the last year that was used. So if you want to use that transmission in your duster you'll have to find an old drive shaft with the trunnion on it so you can Cobble two drive shafts together to make one.
If you pulled a side cover off and inspect the transmission and check it all over real good and it turns out that it is a good transmission it is worth $250. Just not a transmission I would buy to put in my Dart Sport or Duster.