Looks like you found your answer. In the 1974 run, a strike from a supplier caused Chrysler to go to their parts bin and use the 11x2'' rear brake setup from the C body line on "some" A bodies thus having 3 different sizes of brakes on the rear.Most known were on the 8 1/4 axle. I found this out from a parts manager at a dealership and it was also a article printed in Mopar Action Magazine. A friend was parting a 74 Dart that I got the rear from,,I too found out the hard way. Bought drums,shoes and hadrware for the 10x2 1/2 tried to assemble and "What the H#!! ?"