Def not OEM Z32. Any more markings on it? Definitely a R230 diff? Not many aftermarket centres available for them.
OP is right, it is a 1 way. Looks similar to a Cusco RS but it's not, unless it's a very old model. The plates don't have the oil flow indents in them, and most Cusco are dual option, ie 1.5 & 2 way or 1 & 2 way. You can set it how you want. This one you can't.