Back to phenotypes for a moment. It might be useful to note that the population of much of the deep south (Va, NC, SC, Ga, Alabama?) remained very stable for a long time.

That is partially true, at least. While families sent second sons and/or went west to Louisiana, Mississippi, Texas, etc., many white southerners have remained where they were "planted" for hundreds of years. (The migration of black Americans and Native Americans from the south is a long and different story, but that is not the group we are discussing.) As Jim and David and others have observed, some of this is myth and some is highlighting the (currently) favored ethnic group. And I know before I say so that there are many exceptions, but from the mid 19th century up until WWII, the population of most Southern states had come from the British Isles and pretty much stayed there. (or Africa or Huguenot France...) Sure, many small towns have Greek grocers or restauranteurs (or their grandchildren who are lawyers and doctors,) and there are Jewish communities older than the liberty bell in Savannah and Charleston, but the typical white southerner's physiognomy is completely devoid of slavic or nordic or mediterranean features. That is, when my father went to Ireland in 1985, all he had to do was to put on the flat cap he'd brought with him to blend in with the locals. And a friend's father went to the Shetland Isles (or the Hebrides) and reported the same thing.

Untangling the genealogy a little, I find Swiss Hugeuenots, French Huguenots, Derbyshire English, Anglo Irish from Dundalk, and yes, Scots from East Lothian, all crowding my family tree. Those are the easy-to-identify ones. They all either blend or assimilate into that Southern American type known as Scotch/Scots Irish. By comparison, I have a lady friend who grew up in Buffalo, New York. She has Irish Catholic ancestors on all sides. And she and her siblings live In SC as part of the great Post WWII change, but they do not really look like South Caroliinians of a generation or two ago- and neither do my friends who came here from Poland in the late 50s, or Cuba, or God Save Us, New York City.

So maybe the locals at Knocktopher could spot my father as a Yank, and maybe his small stature wasn't quite enough to let him pass as one of Kilkenny's own, and maybe the locals in the Shetlands know their neighbors well enough to spot a stranger, no matter how familiar his cheekbones, but they all looked like our cousins in the pictures.