It seems very common that names were indeed butchered in translation when people emigrated to America. Especially if the newcomers could not read or write their own names and spoke with "funny" accents. The registrars here in America would likely have written down the names as best they could, perhaps spelling them phonetically.

McNurlen sounds to me like it could be one of several names associated with Macnaughton. There's a long list of names here: http://www.electricscotland.com/webclans/m/macnach.html . Perhaps it would have been a 'butchered' version of one of those?