A guy that big who knows how to punch will generally hit VERY hard. And as Toxic has pointed out, Hendo throws with his whole body. Gustaf throws straight and picks his shots, dropping people with timing and accuracy... imagine if he punched like Hendo and landed it.
Gustaf hits hard, end of, and I'd pick him to (T)KO Hendo.
You think Gus can do what no man has ever done? I think you are insane. Hendo's jaw can take anything Gus has to offer. I don't feel as confident the other way around. Gus could very well win, but he wouldn't TKO Hendo, not now, not ever. Gus won't even crack the top 5 in punching power that Hendo has faced.