Scratching my head???

I am restoring a 74 Duster with a 318. It had a 904 trans but has been switched out for a over drive cast iron case 4 speed. I know I have to get a different yoke for the front of the drive line but the one I got today was wider in the u joint area than the one for the 904. Can some one educate me on what I need to do. I hope to convert to a 8.75 rear end in the future but want to get the car running with the 7.25 to start with. Can the 2 coexist? I realize I have to get some drive line work done but what?