differential?

I have a 97 trans am A4...correct me if I'm wrong, but I think I have the 7.5" rear right? I think I have 2.73's right now and would like to change to 3.73's, but I don't want to have to pay the 700 bucks to change to a series 3 carrier. I was looking at richmond ring and pinion sets from summitracing.com and they say they have 3.73's for a series 2 carrier? How could this be? and would it work in my car?