BBP 7 1/4 backing plates to 8/34

Trying to get some information for my father. He has a 73 Dart sport with a 7 1/4 with BBP . He is thinking he can use the 7 1/4 BBP backing plates on the 8 3/4. His goal is to retain the wider brakes and the bog bolt pattern. My goal is to avoid him getting started on something that will not work. Anyone have any information on if this swap is possible. He plans to have moser make up axles for him.