"Wikipedia says the original title of this poem is "Dark Haired Myriam Ran Away". It was changed by THE DUBLINERS when they started playing it. Is anyone familiar with whether this is tue or not."

It was originally called that. Peter Kavanagh (Patrick's brother) said how although it was based on Hilda Moriarty, Patrick used the name of Peter's girlfriend as a cover. That was on its first publication (I think in The Irish Times, sometime around 1946?). I don't know about The Dubliners changing the name - it is referred to as "On Raglan Road" or "Raglan Road" in Kavanagh's poetry collections. I presume it was just on its first publication that it was referred to by the Miriam name?

As well, someone mentioned whether Kavanagh himself or The Dubliners had put the words to the air "The Dawning of the Day." I'm pretty sure it was Kavanagh. He also mentions the air elsewhere in his poetry (e.g. in "Inniskeen Pipers Band" I think the poem is called).