The problem is if you have the Eaton rear axle 4.10 is the best there is. The Eaton has a removable pumpkin, and is the most common rear axle 3/4T and up. My 68 3/4T had a Dana with 4.56 and leaf springs. I replaced it with another Dana that had 3.73 from a 73 that had a BB and auto. The biggest problem was shock mounts. The good news is that if indeed he has a Eaton 4.10, he can sell for what the used rear axle will cost. There are a few on this board that dearly love to get there hands on it. I have 4.10s with a A833 stick and 4th is an OD, I love it. I'd look for a 700r4.
Larry
