Pretty neat computer work there, would like to see something like this in the flesh, but I'm guessing that will never happen. But it would look good at a trade show if a combination like that was driven in.
The weight isn't an issue as the base truck in cab chassis form as depicted, has approximately 21500kg capacity before GVM is reached. As an aside, the base truck as depicted, weighs more than the GVM of the top truck by close to a tonne; which really puts things into perspective. My avatar is the truck on the top of the pile...............
Rear overhang would be an issue as I did some quick calculations after checking the dimensions of the FY series bottom truck (I presume it is an FY series). Approximately 1200mm rearwards of the end of the chassis rails is the maximum legal overhang.
Meaning the NPS 300 4x4 light truck on the top, is a tad too far back.
The weights and measure bloke, may not be tall enough, to measure it, so it may be OK 
