Mike Parkes was 6' 4" (1.93m). Dan Gurney, Troy Ruttman, Carel de Beaufort and Christian Danner are also said to be that height

Mike Hawthorn 6' 2" (1.88m) was the tallest World Champion

I can't find anything definitive on the shortest - Alain Prost, Jackie Stewart, Peter Gethin and Tazio Nuvolari are often mentioned