75 Dart Sport - What rear? What wheel pattern?

I agree with TrailBeast. In a ‘75 with a /6 I would definitely expect to find a 7.25 rear axle. As late as it is I would also expect it to have the 5x4.5” BBP with disks up front, but if it’s a stripped down base model it’s possible that it could be a 4 wheel drum car with the 5x4” pattern.

My ‘74 Duster was a very plain, low option 225 /6 car though, and even it had manual disks and a BBP 7.25.