1990 was the first year with 1991 with the stickers. Look at the RPOs in the glovebox. 1990 was also the first year of composite headlights and the nice bench seat with armrest.
Back then I'm pretty sure all it included was cranked torsion bars, skid plates, 3.73 gears, and an ATF cooler.
The Z71 package was supposed to be an iteration of the Sport package back in the SFA. Back then it included buckets, 31x10.50 rubber, skid plate, ATF cooler, and heavy front springs with the 1.25" diameter sway bar.