Also take a look at an article from Snowmobiler's Race & Rally from 1974/1975. A great article on the Corbetts.
Ian on the track at Eagle River in 1974
Kawartha World Cup 1974
Kawarth World Cup 1974
Ian, March 1974.
Here is a poster of Ian from the World Cup. This was produced by Sno-Jet and sent out to their dealer network.