THank you for your reply. You did a lot of work on my behalf. Someone else did some research for me and learned that the neighbors in CHicago were not brothers. Yngve Nedrebo also discovered that fact.
Someone sent me some information that this Oliver Olsen went into the military in Bergen. I"ve been trying to find that e-mail but so far have been unsuccessful. Possibly he moved to Bergen when he was quite young. Unfortunately there are no census records to record that fact. I do have a 1865 census record showing an Oliver Olsen living in Arendal. EVerything matches what my cousin knows about him. He was 25 at the time and was a Smedsvend. Young men had to travel to learn a skill. He had his birthplace as Bergen.
Thank you again. Yngve Nedrebo also told me that he had found an Oliver Olsen in Sogn og Fjordane, but he never got back to me. He's a very busy person. He found an extremely valuable record for me once before--a record that helped me prove that my g-grandfather had changed his name.