As far as I know all gtr diffs are mechanical LSD (or active (v spec)) and Gtst diffs are viscous, so i think you probably have a gts diff .GTR has 4.1 ratio same as manual gtst, autos have 4.3.Gtr s have different size splines in the diff and rear hubs and bigger axles.So to fit Gtr diff yo will need to get all the parts. If you pull the shafts out of the diff one will be a lot longer than the other and have two seperate splines on it if it is a viscous.