In step 9 you don't need to catch Heatran. I was using Snorlax with Stockpile, Belly Drum, Earthquake and Thunder Punch to defeat all NPCs. I defeated Commander Mars and also 99 lvl Heatran. After that you talk to Buck, he teleports you outside the cave and gives back Master Balls and Rare Candies. Now you can come back to Pokecenter, take the Synch Pokemon and go back to the cave and there will be 30 lvl Heatran which you can easily catch with Master Ball.