In 1990 census of names there were 392 GURSKIs in Poland.
The name change came several years AFTER your ancestors were in America, most likely when they applied for citizenship. The manifests were written at the port of departure.http://maxpages.com/polandwww.kuijsten.de/navigator
Have you his place of birth?
Sigmund GURSKI arr. in 1905 from Konetz. www.ellisislandrecords.org