Gear Ratio

I found a 3.31 in a 65 plymouth /6 3 speed,(741) never heard of such,looked it up in the FSM,sure enough,,optional ratio. I just got a 1958 1/2 ton 8 3/4 truck rear complete that has 3 something gears. Have not pulled it apart yet to see actual numbers. Carrier # 1820657 also a number that was unknown (to me).Maybe it is a 3.58 too.