3 series or 2 series?

alright i have a 98 trans am and i want to put in a 3.73 gear. however, i do not know if i have a 2-series or 3-series carrier. i contacted SLP and they said if i have a 2-series i can still get a 3.73 gear but a 3-series carrier would be better. how do i find out which series carrier i have? and if i have a 2-series carrier would it be worth it to get the 3-series knowing that i will be doing more future upgrades?