Other than giving the cooling system a good clean out (as suggested) and then adding new coolant, I doubt you will have any problems. LRs are plentiful in Australia and I've not heard of any cooling issues with them since the 6 cylinder petrol engines of the 1980s.
Bear in mind that we (in Oz) often get temps in the high 30s and low 40s and that vehicles sit in traffic with ac going full blast, I doubt that you'll get that sort of problem in Mongolia.
If you feel really worried then fit an audible over temp alarm, check the radiator for problems daily (seeds, dust, damage, etc.), carry some concentrated coolant to top up with - never mix coolant brands.