We killed this guy last night, and wow, is he tough! My group consisted of a 49th mage, 48th druid, 43 and 45th warrior, and a 40th ranger. He resisted everything my mage and druid threw at him, and resisted my Ykesha proc everytime. We ended up chaining the mages pet to kill him, with only 2 casualties in the group. This was very effective, and took 5 pets to do. Azdalin spawned immediatly after, and as soon as we got a cleric to rez we killed him. Guller back was yellow to 49th mage, and both the named wurms were blue to me at 45th.
Hope this helps, good luck, and enjoy, this is a fun quest to do!
Wolfbasher, 45th Warrior, and leader Of Battle Cry