I cannot think of a realistic way for the best version of Cleveland Williams to beat any version of Joe Louis, let alone the best version of Joe Louis.
Williams would've undeniably beat the Louis of the Marciano fight, who was shot in every sense of the word.
Louis was shot. Age, and especially drugs had taken their toll. His greatest weapon, his right hand was gone, he'd lost his speed, and had greatly diminished reflexes. He even said himself, he could see he openings but was no longer fast enough to take advantage of them. He was done. He was Louis in name only.