1997 is pretty early for dexcool-type coolants. International (Mainly Consumer Ford Diesel Trucks) officially made their engines compatible with HD ELCs during the year of 2001. You may want to check your FSM (The RAVE Manuals). Search online you'll find ALL of them on ONE site covering every Land Rover vehicle.
The 2001 Discovery II I service has the same plastic ring saying to use an OAT coolant, which is a very general statement. There are many brands and types.
It does say, however in the FSM to use a Texaco/Havoline Extended Life Coolant or equivalent. This coolant is the early formulation of the modern Dex-Cool type coolants you see today.
I have heard the earlier formulations had problems and got a really bad rap for sludging and all the nonsense we've all heard about. To me, I think it was the cooling systems not properly designed to be used for those coolants. Incompatible gasket materials or air leakage may be to blame. Although where do you draw that line? Are you designing a coolant for a cooling system or a cooling system around the coolant? lol
I decided to stay away from Dex-Cool and use a HD ELC they use for diesels. They are tried and true with millions of miles logged in many large diesel trucks. They use the same 2-EHA compound as Dex-Cool to help extend the life of the coolant.
I recommend Chevron Delo HD ELC. Goes up to 600,000 miles and 1 million miles with an extender. 6 years or 8 years. One or the other...
Been using that in the Land Rover for about 10k. No overheats, leaks, or fuss. Others from the Rover Forums have used the same HD ELC-type coolants with great results as well.
If you can't find some wording simliar to "Extended Life Coolant" in the FSM, then I would recommend G-05 for the closest compatibility without the stress of Dex-Cool.
I would like to pose a question as well: What if he decided to use Toyota Super Long Life or Honda Type II Coolant? What could possibly be the ramifications considering cooling system metal types and what not?