Re: Marciano and Frazier if they fought in each other's era
I'm doubtful that Frazier would've gone 49-0 under the same circumstances as Marciano. Let us not forget that, in his real career, after establishing himself as champion, he did stagnate and fall out of shape between the first Ali and first Foreman fights. In order to manage a 49-0 run with wins over all the men Marciano beat, you need an unbelieveable degree of consistency, both physical and mental. That's something which all the Marciano detractors who carelessly say "Well, X-and-X would have been 49-0 too if they'd fought in Marciano's era" tend to forget about.
As for Marciano, I think he would do about the same as Frazier did, except he wouldn't let himself go a little and become complacent between Ali and Foreman, and so might manage to win two out of three against the declining Ali.