Shor Son of Shor is basically the only place.
And even there, it's not a voluntary thing:
Any of those words were enough for the treason-mark, and traitors were only met with banishment, disfigurement, or half-death. He had taken the first with pride, roaring a chieftain's gobletman into dust to underscore his willingness to leave, knowing we would follow. He had taken the second by drawing a circle on the House's adamantine floor with his tailmouth-tusk which broke with a keening sound, showing the other chieftains that it would all come around again. And he took the third by vomiting his own heart into the circle like a hammerclap, guarding his wraith in the manner of his father and roaring at the other tribes [...] The loss of his heart is the sentence, "half-death", imposed on him by the other tribes. (Read: the entities that remove his heart in the other myths. True to the Nord tone of the story, here he just makes it into a grotesque gesture of defiance.)
MK will have to severely twist his tounge to wriggle out of lore that is as blatant and clear as this.
Normally MK writes in 'confusion script' but this is one of the times when it is as clear as day and not subject to misinterpretation, what the lore is saying.
Vilnii, your arguments are rather astounding to me, but I think they are primarily fueled by a misunderstanding on your behalf. You seem to be under the impression that people say Lorkhan and Akatosh (and their various names) are identical, which of course doesn't make sense, because they are consistently mentioned as distinct beings. Why would they be attributed with separate stories if they are the same thing? This is not what everybody means.
The thing with Lorkhan and Akatosh (and again, all their other names count too) is that to themselves and observers, they appear to be distinct beings, but in fact they are not. In their shared delusion, they are simply two mirrored fragments of a bigger entity (and so on) that are completely interchangeable when it comes to name or role. It does not matter whether Akatosh takes Lorkhan's heart or Lorkhan takes Akatosh' heart; you can't tell them apart. This is why they are often flipped around while the rest of the story stays the same. This is why the Elves say Auriel (Akatosh) is the good guy and men say Shezarr (Lorkhan) is.
Now let us take a look at the http://www.imperial-library.info/content/morrowind-monomyth, which you quote there. Firstly you should know you are trying to disprove a generally accepted idea by quoting a text written by the person who came up with the idea in the first place. (Having to "severely twist his tongue" is therefore rather hard.) Your entire argument in that quote hinges on a strictly chronological interpretation of two words. (And chronology in some unfathomable god-time too.) The idea, here, is that "barely formed urge" means an urge so grand and novel as to still be largely unimaginable. Even in your other quote, the duality is clear. Akatosh is what allows everything to exist, Lorkhan is his counterpart as the limit of everything: one necessitates the other.
Granted, this is a very old (before Morrowind) text in which many of the ideas we are discussing here simply did not yet exist in their current form. However, the text already abounds in dual terminology, but does not yet -explicitly-extend that duality to Lorkhan and Akatosh. (Though implicitly it does, e.g. "upsetting the status quo much like his father Padomay had introduced instability into the universe in the Beginning Place.")
Let's simply take a look at the introduction alone:
Man or mer, things begin with the dualism of Anu and His Other [...]These twin forces go by many namesIn any case, from these two beings spring the et'Ada, or Original Spirits.Let's not stop here, though. In later writing, the seminal idea that the universe consists of mirrored entities denying each other was developed further, with particular regard to Akatosh and Lorkhan. As per request, I'll make an attempt to quote all passages where Lorkhan and Akatosh's shared identity is made explicit. Virtually all of these are plainly interpretable and without exception all were meant to inform, not confuse. There are undoubtedly more, but these are the ones that come to mind immediately (emphasis all mine):
http://www.imperial-library.info/content/morrowind-annotated-anuadThe Anuad is one of the oldest in this list, being roughly contemporary with the Monomoyth. Notice how the narrative of Lorkhan and Akatosh (disagreement over the mortal world, with an eventual violent death of one of the two) is presented on a different level, with Anu and Padomay. Pay special attention to how it is Padomay (associated with Lorkhan) who stabs Anu's (associated with Akatosh) chest. The location of the wound is a clear anologue of the removal of the heart. We can conclude that even in this ancient text, the roles of the two players can be inverted.
http://www.imperial-library.info/content/morrowind-thirty-six-lessons-vivecThis text contains numerous references to the same idea, but in different incarnations. I will not be quoting from it now, since the explanation would lead us too far.
http://www.imperial-library.info/content/etada-eight-aedra-eat-dreamer
The duality Lorkhan-Akatosh is virtually the only topic of this text:
[...] is it any wonder that the Time God would hate the same-twin on the other end of the aurbrilical cord, the Space God?along its two-headed fighting rays, each refusing their origin pointmassive map-god (holding a compass, holding a timepiece)http://www.imperial-library.info/content/oblivion-song-pelinalThere are some explicit references in this text. Pelinal, who is said to have a gaping wound where his heart should be and is explicitly described as Padomaic (Lorkhan symbolism) says the following:
""O Aka, for our
shared madness I do this! I watch you watching me watching back!"
In the final song, Pelinal miraculously appears at Alessia's deathbed and comforts her:
[Let us] now take you Up. We will [show] our true faces... [which eat] one another in amnesia each Age."Compare this to the version presented in Oblivion, where it is Akatosh who appears at Alessia's deathbed.
http://www.imperial-library.info/content/shor-son-shor-fullI cannot quote particular passages from this text. All across the text, characters shift places and die to inexplicably live again. Notice how Shor and Ald, his counterpart speak the exact same lines.
I am certain I have forgotten some. Feel free to contribute, anyone.