Hello Whitethorn, as you state there is no birth for Francis nor marriage of the parents, however I did find three children to those parents from 1835 to 1841, they are Nicholas baptised 20th Sept 1835; Bidget baptised 19th May 1839 and Thomas 1841 baptised 11th April, do you know if these are siblings of your man, the address given in two of the baptisms is Ballykelly which is in Inniskeen, there is a site here about Louth, it says unknown in the other one, There is a Louth site here and if you see any references you can revert as I can access most of them, there may be a headstone but bear in mind most could not afford one.
There appear to be a lot of Byrne and Hughes in the area also. http://www.jbhall.clahs.ie/index.html and to assist in locating townlands I find this site a great help, bear in mind this is a civil record and may not exactly agree with the religious division. https://www.townlands.ie/louth/ ;
I find it odd that someone would know that there was a Newport, Mayo without some knowledge of its existance, I searched for the marriage nationwide and came up with nothing nor a Frances father Nicholas 1820 to 1840.
Oddly I have been assiting a lady whose ancestors left from nearby circa 1838 and by a stroke of luck located some headstones (someone sent me a photo of headstones) in NY state with info on them and a possibly obiturary if you think searching will assist for more US records.
Pat
Good Luck
