Lets be honest, that fight is not easy to heal if it lasts very long. You mentioned you had a 24k PT in your group and an assassin damage dealer. Already you are in for a treat because of lack of damage from the Powertech and the assassin won't do 3k to balance out the 1k damage the powertech will do. . When I healed that with my sage and scoundrel the first time we wiped 5 times to realize we were borderline on the enrage timer. This was a few days after the 2.0 patch came out.
With a better group you will have no issues healing it as the damage output will be better. The fight shorter and the overall damage received from the boss less. When I tank that boss even in BIS 72 underworld, I use resilience on every second bashing. The boss has a shorter time between abilities than my resilience. So 1st resilience, second battle readiness, third resilience, nothing, 4h resilience, 5th battle readiness, etc.
There is a position behind the boss as you tank him with your back agains the wall where he spawns where as a healer you will not take any damage so less heals on yo more on the raid. Sadly, the boss has a stupid mechanic where he knocks the tank in the wall or left/right, even thru resilience. You need to get closer and when you see the smash cast, hot the tank quit and yourself, if in range of the ability.
Sorry about the lack of clarity, slept 4 hours and had no coffee today