I have used two different shops over that last several years for head gaskets on two of my '04s.
Carsmart on Watson and Laclede will do great work but they charge book time, so are fairly expensive.
I also used Reid Vann on Manchester on my other '04 (which I no longer have thanks to a u-joint grenading). They were less expensive but also less responsive to inquiries. This '04 also started to leak externally from the head gasket two or three years after the work was done. Not sure if that was a quality of work issue or just bad luck.
The head gaskets done by Carsmart were done in 2017 and have lasted over 100,000 miles. Yes, I drive the Discovery a lot. If you go to Carsmart ask for the mechanic/tech, Chris to work on your Discovery. He knows what he is doing on these Land Rovers.