forgetting about specs..i used 0w20 liquimoly in my high mileage lr4.
purchased the car used with no oil leaks.
about 1 month later I changed the oil within and week i developed 3 oil leaks. rear main seal, oil filter housing gasket, valve cover gasket.
replaced the filter gasket and changed the oil the Valvoline 5w20 Maxlife synthetic....oil leaks stopped.
just wanted to share my experience about 0w20 weight.
anyway, i doubt spec is that important. any quality synthetic oil should be fine, as long as you are changing 5-7k miles. which you should be doing anyway. the extended OCI that LR suggests are a little long, which is also most likely why they had a very unique oil spec.
and I would suggest walmart for oil. they sell a good variety in 5 quart jugs, which always seem to be better priced than any other retailer, especially one selling quarts, or cases of quarts.