I recommend using Ferrothorn and Heatran together in that team. Replace Stealth rock to Rapid spin on your Excadrill. If you cannot do that, you might toss in a Rotom-W or Mantine as 6th. Otherwise, the 6th Pokémon could be a priority attacker. Most of the players go with Conkelldur in that case, considering you already make a decent core with Tyranitar and Excadrill (incl. Heatran and Ferrothorn [which has spikes]). Although, I recommend you either Staraptor or Gliscor(defog is legal now on it) for the 6th place. Breloom works well aswell.