It appears that there are doubts from some quarters concerning the suitability of the California for this type of adventure.
I have no problems with the capabilities of the California for that sort of journey. We did the aforementioned 28,000 miles through all the Americas in ours and it was as good as we could have had any vehicle - believe me, all 3 parts of the Americas have horrendous roads (yes, USA as well!) and although we saw people with Unimogs, MANs, Steyers and Army Volvos we always got where we wanted to go. Ours is all standard 2 wheel drive with road tyres - not even a potty! The roof went up and down every night and although we had to replace some screws from the mechanism it never failed - and we were travelling for 7 months.
There are things that need modifying for most Californias in the UK, the main one being the particle filter, it is simply not compatible with the poor fuel you will find in underdeveloped parts of the world. There are ways around it, even if they are not compatible with emissions in the EU.
Another essential is NOT having fancy wheels and low profile tyres.
There are plenty of things that can be done to make the California as good as most off-roaders, but the standard vehicle is more than good enough to do this sort of journey.
I hope this helps
flyingQ