I have some idea how to pronounce the Irish "gh," if only because I've heard my own (original) family name ~ Heneghan ~ spoken during my one brief visit to Ireland a few years ago. (It's a much more common name in the Mayo/Galway area than I would have suspected; here in the states, there are not very many of us.)

My great-uncle Luke dropped the "g" upon arrival in New York, so we're "Henehans" on this side of the Atlantic. In Mayo, our remaining relatives still use the original spelling, of course. There are folks all around the west of Ireland who spell their name exactly like mine ~ including the owner of a busy pub on Westport's High Street ~ but they're not kin to me, and they're relatively few in number. There are many more Heneghans than Henehans in the national telephone listings, including my cousins who live on the farm from which my grandparents emigrated, as well as quite a few others.

In the US and worldwide, there are many Irish surnames ending either in "gan" or "han"; I suspect that most if not all of these names originally included "ghan" as the final syllable, until the inability of English-speakers to pronouce that dipthong resulted in people choosing either the "G" or the "H" rather than trying to continue using both!