my 97 z28 has the 3.23 axle ratio and the abs brakes,i'm going to to change it over to 3.73 ratio but i'm not sure which series differential i have ? any help would be welcomed!! thanks

 

If your car left the factory with 3.23 gears (GU5 on the build code tag) is has a 3-series carrier. But you indicate your car has an M6???? The M6's (94-02) only came with 3.42 gears (GU6), also a 3-series. Or did you do an A4->M6 swap?

Only the 2.73 geared A4's (GU2) use the 2-series carrier.