McWilliams is interesting because, although a Catholic and a hedge schoolmaster, he wrote in three language registers using Hiberno-English, English and Ulster Scots and suggested tunes from the same three domains.

My 1997 article: "One singer, two voices: Scots and Irish style song in the work of the mid-Antrim poet and song maker Hugh McWilliams (fl 1816-1831)" in Thèrése Smith & Micheál Ó Suilleabháin (eds.) Blas: The local accent in Irish traditional music Dublin & Limerick pp. 73-99, deals with this aspect.

In fact "The lass among the heather" was so successful in its Scottish voice that when the Glasgow Poet's Box printed it on a ballad sheet it included this note:

Glasgow, Poet's Box [Saturday morning, 26th Nov., 1859]
Blooming Heather [Price One Penny]

"This splendid piece of Scotch colloquial poetry is one of the most touching and sublime of its class. The eloquent and sublime outpourings of the love-stricken swain are here portrayed in that sweetness of thought and expression which can alone flow from a tender and affectionate heart. How to woo and how to win is a problem which has puzzled the brains of many a thousands youthful lovers; but now their hearts may be rejoiced and gladdened, for they will here find this great problem solved. Haste then, ye who would win the tender affection and love of the fair sex, and obtain copies of this sweet Scottish song. It can only be had at the Poet's Box, 6 St Andrew's Lane, off Gallowgate, Glasgow."