That would explain it Richie. Great photographs, there seems to be two types, some with the traversing cranes in the middle of the wagon and the others, like the 3 at Adelaide, with cranes at the side of the wagons.
I only have Doyle & Hirsch 2nd Edition, and it shows the 24224-40 Rail Trucks without cranes. Maybe they were a later addition. In 'Traction & Travel' 4th Edition they list under Departmental Stock, 5 Flat Wagons No's 654A-658A but no description, another type of bogie flat?
Thanks also to GM 171 kk, great Time and Motion video.