pull all the cases off, til youre looking at the gear stacks.
look at the center diff. if it has the mark in the gear teeth, its a 92-99 center diff. if no mark in the gear teeth, its the 89-91 style.
if the 3-4 shift fork has 3 holes and travels through all 3 shift rails, its a 93-99 transmission.
by chance, if you really lucked out, you'll pull it apart to find the mark in the gear teeth, but the 3-4 shift fork will only ride on two rails. this is the badass late '91 - '92.5 transmission. no weak 3-4 hub & slider. evo 3 stuff will drop right into this transmission.