Patrick Galvin on Irish Drinking Songs, Riverside RLP-604, is evidently the Clancys' source. He does a rousing uptempo "Moonshiner" pretty much identical to, and earlier than, theirs.

In his notes he says only that the song is well known through the English-speaking world, and that the American "Rye Whiskey" is well known in Ireland and England.

I take this as presumptive evidence that "Moonshiner" is an American original, and not Irish save by adoption. (Still it's worth covering all bets by continuing to search for any Anglo-Irish song that might be an ancestor, however unlikely that now seems.)

Bob