I'm fairly certain he was on there between the other two, maybe 5-6 years in the mid-70s. And of course, RIP Alec.
Edit: http://en.wikipedia.org/wiki/Nash_Roberts guess it was only 4 years. Was around when I first started actually watching news with my parents though I don't think I got much of it. His brother Ep ran the astronomy shop where we used to get our telescopes and binoculars. I think maybe around 80-81 near Lakeside.
Anyway, I still can't remember who was on 6 while Gifford was still on 8 :( I think WGNO used to have the afternoon cartoons, don't remember them doing news back then.