You definitely don't have to have a specific body type or build to compete in and be successful in strongman. The great thing about strongman is that the variety of events cater to all body types across the course of a contest. Certain events will favor athletes that are shorter (pressing, deadlifting), while others will favor those that are taller and have longer arms (carrying events, atlas stones). A body type somewhere in the middle is going to give you the best overall inclination, but hard work and dedication towards being well rounded will make a greater difference than anything related to your body type. The more time I spend in strongman, the more I realize that specific skills and their development are just as critical, if not more critical than overall strength and body type.