The VR loading gauge, as it used to be, and probably hasn't changed all that much, can be found in any WTT Addenda. Victorianrailways.net has one of these:
The link takes you to the page but you have to scroll down to the fifth group which has the May 1983 version; go to page 46 to see the loading gauge.
I was 3 mm under (1.5 mm each side of the centreline)
in the width and 5 mm under on the height!
Thankfully, I didn't launch into width at height but it looks like it has been increased to cater for higher containers. Say 9 foot (2744 mm) on a VQCX at 1111 deck height = 3854 mm high x 2590 mm wide.
Only an inch or two here and there ......................... oops crunch ..........
Jumbo flats should be just about OK. Apart from the CUBE Maryvale flats are there any jumbo flats still on BG?
I like the comment about loading up to 1220 mm being secured - after that it doesn't matter !!!
It is this unnecessary sort of instruction that lawyers love these days.