Marciano by late stoppage ko ,but at some point he'd be getting tagged by shavers bombs. May find himself in same place as Holmes did so it's not a Don Cockell type fight . Marciano wko Shavers 14
I think the length of the fight would be a function of how much respect Shavers has for Marciano. If Shavers has little respect and jumps on him like he did with Quarry the Rock might get rid of him quickly. Marciano's defensive skills are underrated by many and he had an iron chin.
Marciano on pedigree. Shavers always has a chance with his bomb of a punch but he lost too many times to mediocrities for me to pick him over a machine like Marciano.
Shavers hated taking punches and did not throw volume like the Rock, so I will go against the grain of talking about stamina to say that Marciano in 1.
All four of the fighters you mention were stand-up fighters. Marciano crouched and leaned to his right which would allow him to duck under Shavers' right. He also kept his guard up as he worked his way inside. Ali and Holmes ultimately won their fights against Shavers. Holmes was dropped near the end of the fight when he was slowed by fatigue. Against Marciano, Shavers would be worn out as the fight wore on and I believe he would be stopped well before the end of the scheduled distance. Ellis' style was based on hand and foot speed. He had slowed considerably by the time he fought Shavers. I know this because I saw the Ellis' fight against Boone Kirkman. Norton got caught cold, so I can't say much about that except that Marciano would have to be careful in the early rounds. Walcott and Moore caught him with right hands early so Rocky would have to be on the lookout, but they were cagier fighters than Shavers. One thing I can't get out of my mind is how gassed Shavers looked in his fights against Roy Williams and Holmes. Marciano was relentless and he would have taken advantage of this situation. Also, in looking at some clips of Shavers against Ali and Holmes, it appears to me that Earnie needed room for his power punches. Once Rocky wore him down, he would be on top of Shavers denying him that distance. Anyway, McVey, that's my take.
Excuse me for not investing in this recreation of Marciano as defensive wizard but he got nailed early and hard in his fights with Walcott and Moore. If Shavers nails him early, that could be all she wrote.
Moore 39 and Walcott 38 found his chin and floored him, I'd have to give a prime Shavers a chance of doing the same.Wouldn't you?
Norton wasn't a stand up fighter really. Walcott knocked Rocky down with a left hook. You make a decent case I'm not 100% convinced but it is a scenario I can see occurring.