Defeat Joshua and Usyk impressively (in Usyk's case, this would require a trilogy as he's already lost the first), blow through several top contenders like Dubois, Parker, and the like, and maybe beat a touted up and comer like Itauma. In short, it's not gonna happen!
I'd suggest thats disrespectful towards the elder statesmen of the game such as Muhammad Ali to speak.
He is perhaps the greatest bi-polar God loving steroid cheating heavyweight gypsy fighter in my lifetime
If he had stayed active after the Wlad fight and beaten Wilder, Usyk and AJ plus a few more top contenders he would have been very highly rated. To be considered the best ever was unattainable for him though as no matter what he did, rose tinted glasses will always favour fighters from previous generations.
Giving Wladamir the rematch and beating him again. Not fighting Chisora for a third time. Beating Uysk easily like he said he would so there would be no need for a rematch. Fighting Joshua and winning Easily beating Ngannou. He should of never of been put on his backside by him. Joshua made it look easy (like it should of been) , Fury did not.