I think Louis could stop Marciano, but I wouldn't be surprised if this went the distance. When they actually fought, Marciano was still fighting in a more upright stance; later going into a more difficult to manage crouch (which Louis looked frustrated by, against Godoy ). Louis was too far gone in his very last fight to be comparable to his former self. A younger, sharper Louis would have had much more in the gas tank and would not have been caught as often by Marciano; suppressing a lot of Marciano's initiative, with the jab, and avoiding more of the punches that made their way into range. I don't think Marciano's overhand right would have found a home very often, if at all. I think also, we would have seen Louis time Marciano coming in more easily; connecting with his short counterpunches, which were still quite powerful, and following up with more combinations than he was able to muster, at the very end of his career.
I agree Marciano a rythym breaker and Prime Louis would fight aggresively. Marciano also had 2 very powerful hands to stop you with, Say what you want but Frazier was a converted southpaw & like Cooney pretty much one-armed as far as power That being said what I said before, tough tough fight for both men & a younger Louis may go in earlier but does not mean he comes out a winner. This fight looks to be brutal