The condition is that he at least fought with the champion. My favorites are: Bruce Seldon, Frank Bruno, and most of all Evander Holfield from the fight with Mike Tyson.
Tim Bradley, Anthony Joshua, Ken Norton. None look like true bodybuilders but maybe in the physique category.
I guess Primo Carnera would fit the category as his physique was huge, cut and defined, in lot of the posed shots he did.
Louis Monaco, heavyweight journeymen from the 90's, who I believe actually started out as a body builder. He probably is really the only one that really had anything close to a real body builders physique.
In the early part of his career, no one his size 6'8 250, came close to the physique of Tye Fields. https://www.profiboksz.hu/images/abc/t/TyeFields1.jpg
