Several years later and wandering through the Welsh saint book, and my stone just might be part of a stone circle and not disputed ;)...
The church was named after Rhian – 5th or 6th century, a follower of St.David. He founded a church here, “probably a wattle and daub building behind an earth wall” Breverton goes on to say..“In Llanrian parish, not far from Tregynon, is Llain y Sibedau (Place of Whispers) a ruined stone circle”
The Book of Welsh Saints.
1849 – Llanrian
“Near the church are some Druidical remains, consisting of many large stones, most of them now broken: they were formerly erect, and, in their arrangement and general appearance, formed in miniature, according to Mr. Fenton, a tolerably correct representation of Stonehenge”.
From: ‘Llanrhychwyn – Llansawel’, A Topographical Dictionary of Wales (1849), pp. 85-98. URL: british-history.ac.uk/report.aspx?compid=47856