Dave,
I have been in correspondence with Jane Mylchreest of Colby Isle of Man for a number of years.  
In 1979 the Costain's of Colby got together and drafted a Costain Family Tree starting from John Costain d 1717
I now have the whole Tree on a PC Family Tree, in excess of 900 Costain's.
Let me know if your family originated from Colby

Regards,

Alan costain.