I have found one Jurgis Gustainis in Ellisisland database, 21 years old, who arrived to USA on 05 of May, 1909 on the board of SS "Friedrich D Grosse" and was going to Minerville, Pa. His father was Juozas (Joseph). Is this the same Jurgis Gustainis you are looking for?
I have heard about writer and politician Valentinas Gustainis (15,July,1896-11,Oct.1971) who was born in Vinksnupiai village, Vilkaviskis district. Is this the same Valentinas?
And have you heard about Donna Fuller who lived in Murrieta, CA about 5 years ago and may be lives there now? Her grandfather? was Gustainis too.