Fraser would win by points in a similar way to FOTC. Marciano has a better chin and that is the reason why he would not win by knockout. Frazier has superior head movements, and is never knocked out to count to ten. It is likely that Frazier would also be knocked down, but whoever gets up Foreman 6 times, I believe Marciano would too. Marciano is not Foreman ('73,), and it is this fight that makes me wonder: "Does Marciano have a better chin at all? What a war that would be, huh.
Tbh i'm not sold on that idea. Marciano never fought the caliber of fighters Frazier did, nor the punchers. Old Louis, Walcott & Moore were the hardest punchers he fought - 2 of them former LHW's (both who conviently dropped him). I'm pretty sure Quarry, Bonavena, Chuvalo, Ramos, & Foster had around the same or greater punching power than Walcott & Moore, & better punching delivery than a shot Louis. Had Marciano fought Foreman, who's to say he wouldn't do worse than Frazier & maybe not be able to get up from getting knocked down like Frazier did. I believe you've just answered your own question. This is the most plausible explanation for Frazier & Marciano's chin's.
Calling Walcott a former LHW is like calling Ali a former LHW because he fought at that weight at amateur level. Walcott was natural HW. Is it possible to fare worse to be honest?
Well truthfully it was a perfect counter with all his momentum working against him. Archie was a clever, clever man. I am quite sure Rocky was only ever knocked down twice and hurt early and always by smart guys with heavy hands and it was for only a few spots to shake off the cobwebs.
Which is the same size Quarry and bigger than Foster. Bonavena and Ramos had 10 lbs on Walcott, that's nothing.
A very accomplished expansion on your hypotheses, and in doing so have sort of bought me onboard, well done. Trying to stay on point, your thought process has given me a inkling as how the fight might play out, Frazier for almost all his career would have been fighting men of 14st plus some as heavy as 15+ ( Ali/Foreman/Mathis) as opposed to Rocky, his contemporaries were around the 13.8 mark, he himself stayed at 185ish for most of his career, the extra 20 pounds or so that Fraizer weighed , I believe would have played a part in who would be feeling the the other man's punches the most, so yea, they very well might be feeling the pace by 7/8 rounds, due to Joe throwing lots of leather ( Rocky less so ) and Marciano being on the receiving end of shots coming from a fighter to whom he conceded a lot of weight. Enjoyed this, stay safe buddy.