I might be late on this but better late than never ... ;-)

Gr. Zunder sounds like "Gross Zuender" - wich is now called "Cedry Wielkie" in Poland. Just check

http://www.westpreussen.de

though the website is only in German language. Though Wikipedia & Co should have some information on this town and it's history too.

In regard of the Hamanns - I know of a Anna Margareta Hamann (nee Fälber) who was living in New York in 1863. Does this sound somewhat familar to you?