Maxis are significantly narrower than Landcrabs so you can't just put the front of one on the other. That Maxi ute has had an awful lot of work for no apparent reason when you could buy an 1800 ute off the shelf.
I'd say the NZ plate is the reason that this conversion occurred - partly because Kiwis like(d) a DIY challenge and partly because up until the late 1980's, cars were not easy to come by, so those that were around kept their value and damaged ones would be rebuilt if they could be. Chances are this Maxi may have been such a case, as it is registered as a Maxi, albeit it a 5 door one in blue/green!
Utes are also very useful things over here and up until a few years ago, car-based ones were just as popular as 4x4s. Here's a few other Kiwi conversions I've spotted at Horopito Motors:
This one looks pretty purposeful!
This Super Minx, not so much.
Someone tried a more modern day iteration with far less aesthetic success but 4x4 utes are mega coin here, so I can see why they gave it a go.
Here's it's grandad, much better presented and a great example of what to do with war surplus. Seen at the Transport and Toy Museum in Wanaka.