I’ve not visited this site, but I stumbled across the following description of the cist on Coflein:
Burial cist, probably Bronze Age, on the lower south-west facing slopes of Cwm Tal-y-braich. A stone built subrectangular cist measuring c. 1.9m from north-east to south-west by c. 0.9m transversely within several large earthfast orthostats up to 0.3m in height. Cist has been disturbed in the past, with what is probably a large capstone lying immediately to the north-west, resting at an angle on the orthostat at the south-west end.
The eight figure grid reference given is SH70606081.