Bought a 70 Dart Custom Parts car and I have a question.

I bought the car because it has a very nice roof skin and front disc brakes that I want to swap over to my 71 Scamp. I was looking at the rear end and I know just about nothing when it comes to this stuff. Can anyone tell me what i have here? I just have a 7 1/4 under my scamp now and I'm thinking this is an 8 1/4. Would that be worth the swap?