About mid 65 Chrysler came out with instructions to replace under warranty 7 1/4 rear ends with the 8 3/4 on all Darts and Barracudas that came with the 273 4 barrel with the 4 speed. Toward the end of the production year they started putting the 8 3/4 as a standard option in 4 speed cars. I have a copy of the letter.