This is the only photo of Cardiff Railway No.6 or GWR 1339. 1339 was a 0-4-0 saddle tank engine built by Kitson & Leeds Company in 1899 with the works number if I have to guest the works number is 3800. It spend most of it's life working with it's twin No.5/1338. It was withdrawn in May 1932, and later scraped in 1934. However it's twin 1338 is preserved at didcot railway centre. Here's the link to the photo I found of GWR 1339: https://picclick.co.uk/Railway-Stea.....924579187.html