Isaac is a very unusual name for a native Manx - likewise a double Christian name was virtually unknown amongst native Manx until mid 19th century though it is possible that Allen here was maternal family name which is Manx - both would indicate to me that Isaac Cain was unlikely to have been born on Mann (if he was then I suspect a search of the IGI should quickly identify likely candidates) - Alabama is not known as a destination for many Manx - how do you know that you have Manx roots ?