Foreman 1 Foreman 2 Louis Liston Dempsey Foreman is the worst matchup imaginable for somebody who can't box off the backfoot and has a glass chin.
I don't know if Joe Louis would really be the toughest opponent which some may assume based on his all time standing. He is pretty methodical at times and likes to be able to pick his shots so that would allow Wlad to keep it a slower pace as Wlad is also methodical and likes to pick his shot. He isn't a guy who would come out the blocks and rush Wlad like a Mike Tyson would. He also isn't as durable or strong in the clinches as Foreman for the posters who are a issue with the clinch and holding. Again this is me taking the Joe Louis that existed in real life which may not really be the hypothetical.
1. Louis 2. Foreman 3. Liston 4. Dempsey Louis is the only one here to have the skill to get through Wlad's jab and unload his combination when he gets close but it would be a rough going especially if Wlad uses his clinch well. The rest simply don't have the same level of skill to have much success against Wlad. Foreman and Liston are too slow and limited. Dempsey has the speed but not the size or the craft to get through to Wlad. Wouldn't have any of them as favorites over Wlad but I'd give Louis the best chance.