If you don't have the 8 3/4 yet, look for one from a 65-67 B body. They will have the big bolt pattern and even though the axle will be wider, you may be buying new wheels anyway. I have a 66 Coronet axle in my 67 Dart. Standard 15x6 wheels clear fine. I have 235 60 tires too.
Your other options include buying NEW axles with new bearings. Prices vary, but they are usually over $250.