This image was just dug up by Cartoon Brew.

http://www.cartoonbrew.com/cartoon-culture/discovered-fleischers-superman-model-was-karol-krauser.html

and I found it over at Robot 6.

http://robot6.comicbookresources.com/2012/07/model-for-max-fleischers-superman-found-to-be-1950s-pro-wrestler/

Turns out that the body of professional wrestler  Karol Krauser was used to design the visuals of the Fleischer Studios version of Superman.

Check out those links for the details on this forgotten knowledge.