I've been able to contact Norman Kilgarif who has a website on Holdsworths and is familiar with their numbering scheme. From the serial number, he believes that the frame was produced in 1980 and that the other frame details support this date. Thanks to everyone who offered suggestions both on and off the list.
Todd Kuzma
Tullio's Big Dog Cyclery
Heron Bicycles
LaSalle IL 815-223-1776
http://www.tullios.com/
http://www.heronbicycles.com/