B body 8 3/4 into an A
The early B body rears are close but in a Dart Swinger you don't have much room to spare and may still have problems with wheel clearance. You can get away with a B rear in a Dart sport or Duster but in a regular dart a regular A body rear is the best way to go. Not sure if there is a budget way to do it or not either. The easiest way is to get a complete A rear and either re-drill the axles and drums to large bolt pattern or get aftermarket axles to get big bolt. Or you can build one out of a C body unit by narrowing the housing and re-splining the axles, thats what I am doing for my 73 dart. If you can get the complete rear cheap enough with the gears you want already in it it's not to bad. Shipping on this stuff will realy shoot up the cost as its all heavy. Check out Moser Engineerings web site under shop services and you can get some ideas on pricing. If your close you can build one up possibly cheaper then buying an original and end up with the bigger brakes.