Here you go, John. The song you are referring to is called "O'Carolan Tribute" and it is indeed set to "Planxty Irwin". I believe the words were written by one of the Furey's. They have it in their "The Furey's & Davey Arthur Song Book" available from Soodlum's. The book says the song is "Dedicated to the great Sean O'Riada without whom the name of O'Carolan would never have come to the surface."

O'CAROLAN TRIBUTE

I sat and I thought of a man O'Carolan
who played for kings and lords and ladies
To near him play O' must have been wondrous
to feel his music played at his command.
And the people spoke of your mighty Godly gift
bestowed on you when you were a boy
for to play the harp with your magical fingers
to compose such music that left no desire

And blind man O'Carolan where is your monument
Build it so high that the world it can see
All the people now have their music
thro' a blind harpist that's helped them to see

O'Carolan's Concerto was your tribute
You wrote it so people could remember your name
The 'Big Hills' 'The Small Hills" was your beauty
a conversation between two hills

And Carolan O' blind man you wrote such masters
To show the people you've found our hearts
And you gave our music a new beginning
And from the people it will never part

Then a mighty man whose name was O'Riada
Awakened the people from out of their sleep
And O'Carolan's music it was a part of him
A man I remember, a man I admired.

he spoke of your with great admiration
He played your music with grace and with style
And we'll remember you Sean O'Riada
We will remember you for a long time.

And blind man O'Carolan
He was your monument
He built it so high that the world it can see
And through O'Riada we can be thankful
He's shown us a blind man that's helped us to see