I stood in the excavation pit and know how large the stone is.
Officially it is 100 tons+ which is the same weight as the Tinkinswood capstone.
Having said that when the sidestone was moved a few inches in 2003 I was allowed on the scaffolding to check the top of the stone for scarring marks to see if it ever had a stone ontop.
I couldn't find any but then if the large stone was reused the side stones might not be original.
On one of John Auburys earliest maps there was a triangular stone that lay in the center of the Cove
now sadly gone, the only remants being the huge burning pit..