Gustav Hansen

I'm looking for my Norwegian relatives. I have my great-great grandfather's birth certificate. His name was Ole, born 20 November 1876 in Ostre Slidre. The father line says: Gustav Hansen Skramstad Ostre Thoten. The mother line says: Barbo Olsdatter Hovi. My GG. Gpa emmigrated to the US in 1886. I believe on the SS Angelo to Manitowoc, USA. He was traveling with relatives: Ole and Barbo Halstensen and their children Kari and Paul Iver from Vestre Slidre. In America, he went by Ole Gustaveson and married Helen Williams. My Great Grandmother was Irene (Gustaveson) Weiland, the first generation born in America. She married a German, Edgar Weiland. I'm having trouble figuring out how to search Norwegian records. I've been using familysearch.com. But I haven't had any luck finding marriage info for Gustav and Barbo. I'd like to see how far back I can go in my search. Thanks in advance for any help!