As far as I know the 1970,71,72 A Bodies got 7 1/4 and small bolt pattern. And 8 3/4 and were small bolt pattern as,well. The a Bodies never got 5x4.5 bolt pattern till 73 model year. And lots of 1973 on /6 and 318 cars still got small bolt pattern till they used up what they had
My 1973 Dart came with disk front and 8 1/4 sure grips 321:1 10 inch drum large bolt pattern.
My bet is,someone took a,73 up A Body 8 1/4 and used it in your car with C Body or Truck/Van 11 inch drums as they bolt right on the 8 1/4.
I have snatched up plenty 11 inch drum set ups from C Bodies and Truck / Vans
Just asked for parts from what they ca me off of.