Another 8.25 question

Ok guys, I'll admit I'm a newbie, hell I had never heard of a Dart before the first of May. Now I've got a 70 Swinger with a 318 the guy gave me. I know I need to change the 7.25 rear. Here comes the stupid question, my father-in-law has a 1988 Dodge Ram 2 wheel drive with a 318 & 8.25 rear, this rear isn't useable for me correct? Go ahead & let the joking begin!