Pally tank and I would go with a resto shaman.

I don't have experience of healing with either (I have a 69 druid and a 70 shaman) but my gut says the shaman might be better for a boxer.

I think a lot of the druids healing is heal over time, so takes a bit of preparation to heal a target. e.g Lifebloom x 3 on the tank and refreshing it.

I know it does have quite a quick heal with heal over time component and a full long heal, but for me the shamans quick lesser healing wave to buy enough time for a full heal might pip it. Not to meantion the earth shield, and natures swiftness big heal for emergencies. Then of course there's a multitarget chain heal (whcih could also make use of natures swiftness).

[EDIT: Whoops, doesn't a druid have nature's swiftness too?]

I'm sure the druid could work - tranquility is amazing but on a long cooldown.

The druid I would spec balance.

I would definitely swap out the rogue for the lock. Easier to multibox - but I don't know if you've been multiboxing successfully with the pally and rogue - in which case keep him.