The only photo I have seen is on page 47 of "Picturesque Dyfi Valley" by Gwyn Briwnant Jones. I bought a copy about a month ago from the tourist information centre in Dolgellau - cost £6. The photo was taken from the far side of the valley and shows most of the workings which are now hidden in the trees. The picture is from afar so not everything is clear. If you find any others I would be interested to here about them.