I was interested to hear of the rescue of these locomotives by Sandstone Estates in August. You refer to them as "Nigerian" type, but did you know that the Gold Coast (Ghana) Railway also had 27 of this type, delivered between 1930 and 1953,the most obvious difference being a larger cab than the S.A. locos.
I lived in Ghana in 1964,and made many good friends on the railway at Kumasi. They were very kind to me and I spent many hours driving these locos while shunting in the yards there, although as a small boy I found them heavy to handle! I attach a photograph taken on one such occasion.
Sadly, Ghana Railways saw fit to scrap all its steam locomotives, and those surviving in Nigeria may have been cut up by now, so I was pleased to learn that Sandstone had snatched these two from the jaws of the scrap man!