Can't directly answer yer question Paulus, but your pic http://www.themodernantiquarian.com/post/27741 could easily be the same stone as this one http://www.themodernantiquarian.com/post/18362 (at least a 200mm zoom) that I saw across the moor to the south.

That'd put it in the area of the '(rems of) chambered cairns' on the landranger, which I guess is the Moss Farm stuff?.

There were fences inbetween & I had the dog & my 'limited in patience with megalithic browsing' partner of the time with me, so I didn't get a closer look at owt but the circles. :^(

love

Moth