G'Day Grendels,
As you were talking about the two heads being positioned inwards, kinda reminded me of the Scene from How to Train You Dragon, where the 2 headed dragon in a few scene's had 1 head pecking the other - like a dominate head keeping the other in line. Might be interesting to pose the outer two heads in a similar way, with the 3rd looking over the other two.
With the third head, have you thought about shaving the back upper half, just to change the joining angle to position the neck higher and out of the way of the other necks when they are posed inwards ?