The big initial question, structure-wise, concerns the 'fallen backstone'. If this monument is still now as it was built as seems to have been suggested, then where does this stone fit in as it is far too tall to be that missing backstone? The flanking orthostats are not earthfast and the assumption by others is that the backstone wasn't either. So you 'pay your money and take your chance' but it doesn't solve anything. For the fallen stone to have come from that position it would have needed to be either socketed into the ground/bedrock by around 2' 6" or the capstone would have to be higher if the stone sat on the surface which would throw all calculations out of the window. There seems to be no visual sign of the stone ever being socketed (but only excavation would solve that) and the only other alternative is that it is not the original backstone at all and that is where my money lies...but as per normal nobody can prove anything with certainty unless possibly a full archaeological survey of the dolmen and site was carried out. The chances of that happening today in this present climate is probaly less that zeroil!! Now where did I put Time Team's number :D