Here's the version in Soodlum's, which is just slightly different from what's in the DT.

The Valley of Knockamure
(Brian McMahon??)

You may sing and speak about Easter Week and the heroes of Ninety Eight.
Of Fenian Men who roamed the glen in victory or defeat.
Their names on history's pages told, their memories will endure,
Not a song was sung of our darling sons, in the Valley of Knockanure.

There was Lyons and Walsh and the Dalton boy, They were young and in their prime.
They rambled to a lonely spot where the Black and Tans did hide.
The Republic bold they did uphold, Tho' outlawed on the moor
And side by side they fought and died In the Valley of Knockanure.

It was on a neighbouring hillside We listened in hushed dismay.
In every house, in every town, a young girl knelt to pray.
They're closing in around them now, with rifle fire so sure,
And Lyons is dead and young Dalton's down in the Valley of Knockanure.

But e'er [ere??] the guns could seal his fate, young Walsh had spoken thro'
With a prayer to God he spurned the sod, As against the hill he flew
The bullets tore his flesh in two, Yet he cried with voice so sure,
"Revenge I'll get for my comrade's death, in the Valley of Knockanure.

The summer sun is sinking low behind the field and lea.
The pale moonlight is shining bright far off beyond Tralee.
The dismal stars and the clouds afar are darkening o'er the moor,
And the banshee cried when young Dalton died, In the Valley of Knockanure.

Notes: This Ballad tells the story of Jeremiah Lyons, Patrick Dalton and Patrick Walsh who were surrounded and killed by the Black and Tans at Gortagleann, Co. Kerry. It was written by a native of Kerry, Brian McMahon.

Source: Soodlum's Irish Ballad Book

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I have the song in another book, The Very Best Irish Songs and Ballads, volume 3 (Walton Manufacturing, Ltd., 1999). Lyrics are exactly the same except that it says "ere the guns could seal his fate," which makes more sense. The Walton book says Bryan McMahon was a Kerry poet, author, and schoolteacher who died in 1997.