MMII has, I think, a Dire Elk. You may want to look at that. Alternately, look at the Elephant in the MM (for a huge animal).
Nitpicking your stats:
HD: hp should be 67
Attack: 1d8 is very little base damage for a gore attack from a Huge animal. I'd make it 2d6.
Abilities: 16 Con seems low...