Rotor size inquiry

I am running the 10.75 from Dr. Diff on the back of my Dart, on the rears, I have the Mopar disc's on the front. I ran this combo on the 69 Pro Street with manual brakes and they work fine. In fact I have this combination on the 69 Dart I now have with power booster, from Dr. Diff. Have no issues at all with it.
This is just my application and you will get other ideas.