The head is a separate entity from the body so there shouldn't be anything in the body weighted to the head and vice versa, however i didn't make the rig so i dunno its intricacies. It's the Eleven rig from 11SC if you wanna grab it and play with it. There are controls fro the breasts but i have not yet messed with them. Wouldn't the breasts move with the upper back anyway though? I mean I know I'll need to put in some counter animation. And with them moving with the head that was me moving the upper back control with the head movement as your upper back tends to do when you move your head. However I do see that it is a bit too much rotation at the 408/426 point so I'll dial it back a bit. That might be the problem with those areas is that i'm just rotating too much.