I concur with the point already made regarding that your rifle sounds like it is not a Ranch model or else it would have the scope mount milled into the top of the receiver. However, I believe that the non-ranch models are drilled and tapped for a side mount scope mount.
I would recommend the 2 web sites liked belong for great Ruger Mini-14 information.
www.rugerforum.org
www.perfectunion.com
Good luck and enjoy your mini.