I would use the more specific taregeting in R&G, personally.
I would go with that, if those rules included hit locations for "brain" or "head". But they omit most of the areas mentioned in Called Shot(Vitals) (Brain, heart, major arteries), so I don't think they're intended to supersede the rules for Called Shot(Vitals).
The carotid artery is mentioned under the "neck" shot in R&G. I'm not a biologist, so I'm not quite sure how you interpret Called Shot(Neck) to be a headshot.
If we need to split hairs between headshots and brain-shots, sure. The called shot says you can specify the brain. I have been calling it a headshot for the sake of simplicity and ease-of-understanding. Should we call it Called Shot(Brain or Spine) when we mean to have it bypass regeneration? Perhaps Called Shot(Central Nervous System)?