Information from url listed above compiled from Michael J. Dubin et al., U.S. Congressional Elections, 1788-1997 (Jefferson, NC: McFarland & amp; Company, Inc., Publishers, 1998.) Print.
Dubin incorrectly identifies Duncan as "Robert B. Holmes."
Source for Popular Vote data: U.S. Congressional Elections, 1788-1997, Dubin, et al. p. 657. Our Campaigns - OR US Senate Race - Nov 08, 1966, U.S. Congressional Elections, 1788-1997, Dubin, et al. p. 657 (http://www.ourcampaigns.com/RaceDetail.html?RaceID=7066) (accessed 11 Jun 2012)