The broadside copy Pavane pointed to was from J.F. Nugent of Dublin, dated "between 1850 and 1899"; the most specifically-dated copies are from Brereton of Dublin, and are dated c. 1867, which is consistent with Scanlan's dates (variously given as 1833 and 1836-1900).  The Brereton sheets, (two issues; several copies of each) for example  The jacket green  give the Scanlan text; there is another issue perhaps also from Nugent, but the image links are broken so I can't tell which text was used.

As to the background of the alternate text, I have no idea; presumably one derives from the other, but it must fall to more informed people than we to take that further.  To my untrained eye, I see no visual evidence to suggest that the Nugent broadside is older than the others.

As Wolfgang says, the lyric has been posted here twice, and is easily found via the "Digitrad and Forum Search".  The other posting is above.  There is also a brief biog. of Scanlan in this thread:  Biography; Michael Scanlan (Scanlon).

Daniel D. O'Keefe gives the tune in The First Book of Irish Ballads (Mercier, 1968); on the face of it it appears to be a Caroline of Edinburgh Town variant, but I'll not swear to it.