Dear Jacob,
You should consult this work:
For amusement, I attach a photo of a somewhat similar stone from East Java at the provincial museum in Sidoarjo: the shape of the akṣaras indicates a date in the 11th c.; no information on archaeological context. This particular stone if of the prastāra type: the alphabet is laid out over the stone. I have been wondering myself what place such a stone would have had in a temple.
Best,
Arlo