Go to Ruger's website. They have a sn look up section.
You can request a owner's manual at the Ruger website.
You can get a manual for free by going to Ruger's web site and requesting it.
You can contact Ruger Customer Service through their website, and/or post a question here.
50-175 USD
Which one?...The Mark 1's and Mark 2's are pretty valuable...
$350-$500, depending on the exact version, and the condition. The rifle is a Number 1, not Mark 1. Only Ruger pistols are Marks.
Made in 1975.
50-250 USD or so
Primarily in the magazines; Mark II has a bolt hol open also
If you are seeking date of manufacture, contact Ruger through their website. Values depend on condition- anywhere from $100-300.
50-150 USD or so