I have a preference for the BFG T/A K02's.............which are available in both sizes;
305/70/16- Dia 32.83"
315/75/16- Dia 34.57"
They are both E rated and I have had good experience with then on Defenders. The front end was looked at recently and ball joints etc look excellent.........This van has only around 40K miles on it.
I expect parts for this van to be readily available (within reason) throughout Latin America but being a custom vehicle can complicate that. My understanding is that the front end and 4x4 components are basically from an F350 which is also a common vehicle there. I of course want everything tip top before departing and will carry a kit of spares
As for the tires; we have a shop that is willing to mount some 315/75/16's (35") to see how well they fit at least stationary in the shop.
If they rub they will rub on the sheet metal pinch in rear of front fender, while turning, potentially while hitting a bump. You'll be able to tell easily.