Since most linnorms are Gargantuan, I assume we want the same here? Here are some other Gargantuan linnorms for comparison...
Stygian Linnorm: CR 16, 18 HD, Str 36, Dex 11, Con 24, Int 11, Wis 20, Cha 22
Sea Linnorm: CR 21, 26 HD, Str 38, Dex 10, Con 29, Int 14, Wis 20, Cha 21
Swamp Linnorm: CR 24, 22 HD, Str 32, Dex 10, Con 27, Int 15, Wis 20, Cha 18
Corpse Tearer: CR 28, 28 HD, Str 36, Dex 9, Con 26, Int 17, Wis 20, Cha 19
Since it's melee-centric, we could probably use the sea linnorm for inspiration, but drop the Cha a bit since dwarves usually have a Cha penalty.
So...
CR 21, 26 HD, Str 38, Dex 10, Con 29, Int 14, Wis 20, Cha 18?