I think that maybe "Swedish Roots" is not the best descriptor to attract the attention of someone who can tease out the Stiddems. At least to me "Swedish Roots" signals a connection to the great migration of the 19th century rather than the small but significant migration of the 17th century. You could try contacting the New Sweden project directly - they are the ones who know the proper literature.
Lulof Stiddem seems to have had his origin in the Netherlands, although the family lived in Göteborg, Sweden for about one generation.
