Possibly his birth record? https://www.epaveldas.lt/preview?id=1679%2F1%2F11&wr=186
As found on profile for Julijonas Prakapas
Need to translate and see if there's good reason for the 10 Aug vs 19 Aug birthday -- was the latter actually Baptism date? Did he choose "10" out of a hat after coming to the US?