mmaaxx,
My builder mate got his 100 series done by creative conversions in QLD. He went for the six wheeler option because the wagons don't have the carrying capacity of the 70 series with just the single axle. I reckon the converted 70 series wagon you've shown would still have a reasonable payload but the wheel base would probably be around 3400mm; about 200mm longer than the 70 series single cab chassis and a bit longer than the 130 landrover (approx. 3300mm).
The Hilux from memory has just under 3100mm, mind you the front axle should probably be about 50-100mm further forward to give a less front-heavy vehicle and better approach angles. Dare I mention the Navara has a wheelbase of 3200mm; this is almost all due to it's front axle being further forward. With standard factory suspension the Navara out-handles the Hilux and I reckon this is due to better weight distribution.
One certainty is that the turning circle would be hideous unless the new 70 series is better than the old.