You can find an online version of the published book of history and genealogy of the Dyrland farm athttp://www.slektsforumkarmoy.no/english/
From the opening page - choose 'County books' from the column on the left.
Dyrland farm is a choice offered in the top central list of farms names from the various parish names of the island of Karmøy.
Your Sivert Magnus Sivertsen appears with his parents, step-mother and 19 siblings and half-siblings on page 5 of those devoted to the Dyrland farm.
Help for translating vital words - http://home.online.no/~otjoerge/files/word.htm
The books about Karmøy were my own first adventure into tracking my own family a good number of years ago. It will take you a little bit of time and practice to understand the Norwegian layout - but when it clicks you will have a whole lot of fun!