Rollon had that very economical physique, all muscle and sinew . . . low body fat. And, he hung it all on a small but well-formed frame. Note his rib cage is expansive and he looks knitted together really well.
He reminds me of some of the MMA guys fighting in the lighter weight classes with the general leanness required to fight well, make weight. Big bulky muscles take a lot of oxygen, not a great attribute for fighters.
You see some of this naturally where a guy is generally mesomorphic with lean body tendencies.
One person who comes to mind with a similar look was actor, Charles Bronson, as a younger man. Bronson had muscles everywhere, no bulges or saggy pecs. His muscles laid tight to his frame as Rollon's did. In a shirt and slacks, a casual onlooker would hardly make out the powerful physique of men built like this.
Thanks for posting the photos!