So take a current fighter, and then match him with a trainer from the past who would either work on his weaknesses or really mesh well with his style/strengths. Also, what would you want them to work on more specifically?
Not sure it would have made him better but given Steward's success with tall guys who could better utilize a jab maybe Paul Williams?
I think a guy like Futch would be better for Williams. He may have had him work the jab without pulling him away from his natural style. He'd have likely had him fight more in the way of a tall pressure fighter like Arguello.
I think Naoya Inoue under Cus Damato would be something really special. He has all the physical tools to be an absolute monster - pun unintended - and Damato teaching him the things he taught Tyson would be insane.