Great photos there!
First though Wales IS on Topic, K&ESR have Gazelle (one of my favourite small locos) from the Shropshire and Montgomeryshire Light Railway, part of which was presumably in what is now classed as Wales. Or close enough!
I made a cigar tin model of a Trojan about 30 years ago, based on memory and on a poor quality B&W photocopy of a photo in a book in my local library, I think it was "Cars of the 50s and 60s", by Michael Sedgwick, and if memory serves the car shown was WSU 816, the one in your pics!
The model is not great, but I really had very little to go on, and absolutely no idea of the rear shape.