There’s a list of Beseler 23C lens boards along with descriptions (counterbore locations) and catalog numbers on this site:

http://www.oresteen.com/bess23c.htm

The 80mm lens will work fine on the flat board (4” x 4” x 1/8”) with the 23C, 23C II, and 23C III. The 80/5.6 EL Nikkor will fit both versions: 8021 counterbore on front or 8023 counterbore on back.