Do you have any approximate dates for your Magnus Anderson Blixhavn? Your guess will be better than mine. Any additional information such as wife's name that might help identify him?
Also, check out the http://www.slektsforumkarmoy.no/english/index.html
site I discussed in the reply to the original poster, and check out especially the Dale farm in Skudenes parish. It is pretty likely your Magnus came from there.
I have a Magnus Blikshavn (don't know patronymic) whose wife Anna was b. 1909 (have information on her ancestors, but haven't identified his). But one problem with the name Magnus is that it is often a second given name, so I might have him under a different first name in my files making it harder to find. Approximate dates will help that way.