No typo....the R160 and R180 are originally Nissan units. Sure they may be manufactured by Hitachi but that is not the key point. The fact is that Hitachi is not going to manufacture a specific ratio unless its in mass quantities. So by crossreferencing the models that the diff. was used on in a Nissan application it may be possible to find a ratio that is not currently being utilized by Subaru.
If you buy a rear ring & pinion from Subaru you will find that quite often the "Subaru" markings and labels are simply printed over top the Nissan ones. Peel back the labels and find the original Nissan part number!