I have seen plenty of Diplomat/5th ave/Gran Fury cars in the yards and have never seen them with anything other than the 11 inch front brakes. The only cars that I have seen the 12 inch front rotors on are the 74 and later Cordoba/Charger/Fury models. They may have been on other cars but I have only seen them on those cars.
Regarding the 15 inch wheels: I dont think that Pre 1970 cars except C body and Imperial models had them. Maybe HEMI cars being the exception. The 83-89 Dippy/5th ave/ GF cars had them, and they had decent backspacing as well.