They were talking about single boom Sandvik DD212 or similar...

They were talking about single boom Sandvik DD212 or similar Jumbo's so able to work within the drive dimensions, obviously with 3.5m x 3.5m drives and portal that will also limit the size of the underground trucking fleet (Cat AD22 size maybe?). All of these smaller undersized mining equipment stuff has the advantages of being able to fit in smaller areas and less mining dilution, but they always have higher operating costs per tonne drilled, blasted and hauled than big gear obviously.

From my reading between the lines - its aways been the expensive cost of increasing mining drive and stope dimensions without diluting your mining head grade that would be the issue here. Obviously, all the old previous historic mining dimensions are great for hand mining and tracked ore carts, but that kind of stuff is in the museum now and not a suitable or cost-effective way to mine in Australia due to labour costs and efficiencies.