Ford Ranger rear end fit '71 Dart?

There is only one way to find out try it. If you dont plan on having a ton of horsepower I think the 28 spline would hold up fine. The benefits of the 31 spline out of an explorer are
1) you can get a limited slip differential
2) extra strength in the axles
3) disc brakes
I'm not sure if rangers offer rear disc or limited slip.
If your ok with drum brakes and an open diff for for it.