I am very reluctant to start all this up again but some of the attempts to impose sense on these lyrics are really highly imaginative. I think Ballygrant is a complete red herring. I think the line "Only for nights......" must have been invented by the Clancys. If you listen to DB's recording that line refers to Carrickfergus and three other places, the last of which sounds like Bally Grine, but it's hard to make them out. Nothing about "nights". Ballygrine(?) is possibly a mishearing of Baile Ciuin.
Then follows the interpolation of the Waly Waly lines which in DB's version talk about ferrying over "my love and I". Thereafter if you substitute "she" for "it" in the Kilkenny verses you have a drunk man singing of his dead love.
DB introduces the song - "And here's Peter O'Toole singing about his native Kerry " so there is no need to associate the song with Antrim necessarily. There may well have been a Carrickfergus on the Clare Fergus.