Thank you, but as I understand, the 8-1/4 has the same 5-bolt backing plate as the 8-3/4. And there were Mopars with 8-1/4 and 9" rear drums out there.
The other thing is that my Dart was very fine with its 9" drums. Even at the German Autobahn and more than 55 mph :D It had a strong running...