A note about Outline Diagrams
Just about every railway company in the world produced diagram books of their locomotives and rolling stock. These were intended for the use of the railway staff so that they could quickly look up the main characteristics of the different types of locomotives, carriages, wagons and cranes in use on their system. The WAGR and MRWA were no exceptions to the this rule. I have never seen a diagram book for the Great Southern Railway (and it ceased to exist so long ago) but it would surprise me if they didn't have them.
Usually the diagrams were much simplified and scaled down versions of the larger, more detailed general arrangement drawings kept in the works drawing offices. It is important to note though that the diagrams only had to be good enough to distinguish one type of vehicle from another and some do contain notable errors. Sometimes a length will have one dimension on the diagram but measuring the diagram will show you that it is drawn at a different dimension. Sometimes the end elevations don't match the side elevation. Things like the number of planks may be drawn for effect and not match up with photos of actual vehicles. Modelmakers need to be very careful when using outline diagrams as a basis for a model.
On these pages I have noted the errors on the outline diagrams that I am aware of but there may be others that have passed me by. An example is shown below where the height of the wagon is dimensioned as 9'-7" but measuring the drawing it scales out at about 10'-6" or 10'-7". Other groups of T class wagons were taller than this group and used this larger height and I think that the original draughtsman just drew them all the same inadvertently. Draughtsmen are only human and everyone makes mistakes.