(I find it odd that they never mention the name Hunslet, but there are several clear shots of builders plates so it's clear what locomotive builder they're referring to.)
-Philip Marshall
They aren't all Hunslets, the diesels were built by Hudswell, Clarke, also of Leeds, and the one being painted green a short way in to the video is a Garratt, built by Beyer, Peacock in Manchester. One of the Hunslet 2-6-2 tanks was bought by the Welshpool & Llanfair Railway in Wales in 1975, after the SLGR had closed.