Dart rear tires

Thanks for the photos. I have a 75 Dart parts car that has disc front and 7 1/4 rear with large bolt pattern. This is the front and rear I'm going to use on my 68 Dart. Do I have to change the complete rear or can I just put the brake and back plates and shafts from the 75 rear into the 68 rear? They are both 7 1/4 rears so I'm hoping to do this to get the large pattern on the rear. If I have to I'll move the springs but it's sounding like I will get by without it. I would like to keep the gearing that is in the 68 Dart has as it's a 2:94 and the 75 has 2:76's. This is going to be a car for the wife to drive but I would like to keep the better ratio.