A-body Disc brakes

The rear end is likely to be a 7 1/4 unless it was a prformance model or had some heavy duty options. The 73 Dart I used for the disk brak parts was a 318 car and still had the 7 1/4. But even if it has the 7 1/4 it will be the larger bolt pattern which will match the disk brakes up front.