Thanks for that. Some of the sources you show are listed in the book I mentioned in my last post. If even I get to the NAM (unlikely) or they get digitised, they would be interesting!!
Splendid pic! The book "Steam Traction in the REs" shows 603 as being one of two McLaren patterns; one of these being a crane engine - probably the other one. Most traction engines in use in SA were made by Fowler.