My ggrandfather's death cert shows his birthplace as Kovno and his father's birthplace as Riga. It also gave his mother's maiden name as Luria, a name with a long heritage in Lithuania and surrounding areas. Tracing ancestors in these areas during the mid-1800s is no picnic. My cousin Amy is doing some of the historical research (thanks, Amy!) and has found a Davidic connection through the Lurias.
Another source of ideas for researching in this area is Schelly Talalay Dardashti's Tracing the Tribe blog. Thank you, Shelly!