This is printed at the bottom of the cover of my copy of the 1904 edition of Páidín Ó Dálaigh by Pádraig Ó Laoghaire. Am I right in thinking that it indicates the price? If that's the case, I'm guessing it's another form of réal - sixpence, but again there's no trace of it in the dictionary. Would glan mean that it's only sixpence, with no farthings added on? (Fadó, fadó you could get a bar of chocolate for sixpence, I seem to remember)
Another thing - in the title there's no fada on the O but there is on the O in the name of the author. It seems that the use of the fada at that time wasn't very regular. In the text it's often missing on sé or mé for example, which I find quite surprising.

raol glan = réal glan = sixpence net.

Go raibh maith agat

By the way, I forgot to ask, is it a word in the Munster dialect, even though it was printed in Dublin?

Yeah, it's the Munster spelling. Réal would give another pronunciation in Munster.

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The dialect I use is Cork Irish.
Ar sgáth a chéile a mhairid na daoine, lag agus láidir, uasal is íseal

Go raibh maith agat