With thanks to smitho, here is a scan of the 1979 Network Map.
Unfortunately my scanner is only A4, so I've had to manually join the bits together, but there's only a few minor gaps :)
(https://www.actbus.net/gallery/var/resizes/History/Timetables/1979/Network-Map/Network%20Map.jpg?m=1338713051)
You can also view this in our Gallery, and find the individual portions of the map: http://www.actbus.net/gallery/index.php/History/Timetables/1979/Network-Map (http://www.actbus.net/gallery/index.php/History/Timetables/1979/Network-Map)