Don't get me wrong I doubt we'll ever see him at WW, but if he was to fight at that weight he would obviously need to bulk up over period of time, his thin waist means he never be as thick as Hughes or GSP, but he would be able to add muscle to his arms, chest, back and legs... With all that done I would back him to beat plenty of guys at WW, to be honest anyone who was willing to stand would have a tricky fight.
Big wrestlers would have a big advantage at WW though.