About the best you can do with the old 10 bolt is 4.10. There were a small number of 3.90s and 3.73s, but I have only talked to one guy in several years that had actually seen one. There is an outfit cutting 3.90 gears, cost was just over $300 for the gears. This was on a thread at
www.myoldtruck.com which is down for maintenance at the moment.
I would recommend either a 12 or 14 bolt full floater from a newer truck. A lot better rear end and you get better brakes. You just have to find one with the right gears and the right width. And you can always buy a u-joint with two cup sizes at your parts store, if needed.