1971 rearend 741 case questions

I tried to talk my son into going with 3.55's but he has himself convinced that he wants to go with 3.23. Even though my buddy with a demon has said many times that he wished he would have put 3.55 in and not the top tall 3.23. Dr. Diff sells new 3.55 and 3.91 sets for the 741.