I've got Irish ancestors in my tree too where the first to be born in the IoM were in the 1840s, their parents being born in Ireland. One family sometimes has their name recorded as McNeilly, McNeely or McNally, possibly due to how it was pronounced. The point I'm making is don't assume this Richard is the one you're looking for just because he's McNally, unless there's other evidence that helps. And don't dismiss similar names that might turn out to be one of yours with a variation in spelling.