U.S. Rock Island Arsenal Improved M14

Does anyone have or know were I can get information about the Improved M14 National Match Rifle developed by the U.S. Rock Island Arsenal. A picture of it is in 'Small Arms Of The World', 12th Edition, on page 156. I also remember the 'American Rifleman Magazine' had an article about it in the early 1970s, not sure which issue. Thank you very much in advance for any information.