Louis was extremely fast at 207 lbs, I don't see any reason to believe that he'd be too small or too slow to compete today.
@Guru88 @70sFan865 Please read the opening post. It's not about how he does today, it's about what he looks and fights like.
The idea of a Super Heavyweight Division is nothing new, really. In 1933, I first heard about the idea as a kid. It was called the dreaded Dreadnought Division then. I remember that clearly because my Dad thought the idea was very funny. I remember him saying that sooner or later some guy under 200 pounds would come along and beat Primo Carnera. As for Joe, his style probably wouldn't be much different than it was then, especially with the same trainer. I really don't see these great improvements in technique people talk about today. I think Joe would do well today as he was. Most of his career was well above 200 pounds so I don't see any problem there. And he wouldn't have that layoff he had from World War II, so that would be a big plus. He'd also have the "nutritional" benefits that today's athletes use.
Bridger unified champ edit: just actually read the OP and follow-up admonishments. re: his style, I think he'd still fundamentally be a stalker-puncher, with a few tweaks in his game to reflect today's prevailing ring habits as opposed to his own day. Nothing major, though, just a few modifications to his stance.