The question is on the highlighted clause in this excerpt from Die beiden Wanderer as collected by the Grimm brothers.
Zwei Tage gieng das so fort, aber als am dritten Tag der Wald kein Ende nehmen wollte, und der Schneider sein Brot aufgegessen hatte, so fiel ihm das Herz doch eine Elle tiefer herab: indessen verlor er nicht den Muth, sondern verließ sich auf Gott und auf sein Glück.
Question
Am I OK to think: ihm is telling me whose heart is in question, i.e. that it is the tailor's heart, and can be assimilated to the dative in expressions like jemandem die Haare kämmen (in which jemandem tells me whose hair is in question).
Am I OK to think: If the context is right, the same clause so fiel ihm das Herz could be about someone's heart falling to another. For example, if Snow White came to the end proposed for her by the queen and the poor heart fell to some beast, so fiel ihm das Herz could mean so fiel dem tier das Herz des Mädchens. The same thing holds for jemandem die Haare kämmen. For example, if we are talking about barbers, jemandem may be a barber and the hair belong to a patron.
Assuming I am OK so far, is so fiel ihm das Herz as standard (Hochdeutsch) as jemandem die Haare kämmen or is it more regional?
On the same assumption, is so fiel ihm das Herz as ordinary as jemandem die Haare kämmen?
Background
For example of the usage of dative in a genitive sense that is said to be regional, see this earlier post--in which Das ist dem Bauer sein Pferd is said to be southern and not Hochdeutsch. (As noted there, it's got a feature not present in the other cases because sein and dem Bauer duplicate the same idea.)
Basically I am imagining three cases. (a) The form of so fiel ihm das Herz is as standard and ordinary as jemandem die Haare kämmen. You can use the form today without sounding odd. (b) The form is standard but not ordinary. It sounds bookish. (c) It is not standard and not ordinary. For example, it was a regionalism even in 1857.
Obviously I don't mean any value judgment when I say Hochdeutsch is standard.
I am happy to get answers in English or German. Thanks!