Hi G
As far as I'm aware, apart from the previously mentioned work by Stanhope White, there has been no formal archaeological assessment of the site since Elgees visit. Elgee described them as a 'quincunx arrangement of ancient menhirs converted into a cross-shaped bield'. He also remarked on the 'cup-like markings' on the central stone.

It is a fascinating place and it's quite a while since I was up there.
I'm afraid I can really offer any other information but it does give me an excuse to take a trip over there and have another look around and maybe add a little more information regarding orientation etc.

cheers
fitz