[PxTx]

I use to use the Summit/Jegs catalog for a quick reference on this type of stuff. A 12 bolt chevy car rear is 3.08-3.90 for 3 series. These days, there are aftermarket gears with extra thick ring gears to run lower ratios on such as a 3.73:1 on a 2 series carrier and also thin ones to run 3.73 on a 4 series.

So if you have stock or stock type 3.08:1 gears, these will work on the carrier being offered.