Thanks guys for your replies, I guess I was hoping someone would recognize those markings. Other pics I have seen online don't seem to have the "S" and the "5" like mine does, and often have markings closer to the input shaft. I figured it may be a "bit of an unusual one", and wanted to check before I made any decisions on maybe changing ratios, and/or getting a LSD center for it. I think there may be some other markings a bit further towards the bottom, its just hard to make them out with the diff in the car, and the glossy finish of the paint.
Thanks for your input!