I think on average you have more benefits with seriously raising the van. First 5 cm are easy, then it becomes more difficult.
You are talking about super custom with 3.0 turbo? Please check your VIN plate for gearbox and model code and post it here.
The question is if there as an easy transfer case to take from Landcruiser or hilux.
However, the most easy way is to raise the van 5cm and then add a difflock in the rear axle. Easier to achieve and quite capable since the automatic will also do some nice climbing.
And trim the plastic front bumper up to the metal, because it gets stuck everywhere when you reverse for a 2nd attempt.