:good Rocky was far more active than Spinks and Roy, so his stamina could definitely have been affected with extra bulk. Like you say, he obviously fought in the 180's because that was his optimum weight.
I have never made fantasy fights based on a hypothetical improved version of Marciano, because it depends on too many assumptions. I do think your position is a little bit contradictory however. You effectively argue that modern fighters are better because they are bigger; they are bigger because they bulk up, and then you claim that those same training methods would not work for Marciano. At the end of the day, you are going to have to decide whether bulking up is beneficial or not. If it is beneficial today, then it would have been beneficial for Marciano. You cant have a situation where he is the only fighter in history, who it would not work for.
Totally agree my friend. If Tua can be a mythical tank with the same dimensions as Rocky, there's no reason at all why Rocky can't be a more successful version. Tua came close to beating Ike and Byrd so Rocky could better that. Lewis mightmight aways be a step too fat but no shame in that.
I don't buy the Tua/Marciano comparison. I watched a lot of Tua first hand in the 90's. He was an immensely thick dude, thick jointed, big-boned guy who seemed very natural in the 220-230 range. Here is a photo of a 23 year old David Tua... https://jumpingpolarbear.files.wordpress.com/2012/06/davidtua.jpg Compare to a 27 year old (correct me if I am wrong) Marciano... http://totallyhistory.com/wp-content/uploads/2013/10/Rocky-Marciano.jpg I just haven't seen a single photo of Marciano where he looks close to what I saw first hand in a mature Tua.
I know you weren't addressing me, but if I may: In Rocky's time, 185-190 was his best weight. His opponents weighed mostly around this weight too, and heavies back then needed endurance more than size and strength. Today, the game has changed. Nearly every guy today focuses on size, weight and strength. Rocky today would need to add weight, no doubt in my mind at all about that. The problem is, is that he was not especially quick at 185 or so. Adding 20-30 pounds of muscle/fat would not help him at all. He just wasn't a big man, whose frame and style of fighting could accept that extra weight and make it work. He was short, short-armed, and not as massive in frame as a Tyson or Tua. Extra weight on Rocky might not have a lot of benefit for him.
If it weren't for their facial features, I'd have a very hard time telling them apart in these pictures.
One thing I must say though, in fairness to Rocky, was that he was 100% natural. The guys today, and for the last 20-30 years, were all taking PEDs.
In that case there must be a lot of fighters in the modern era, who are not helping themselves by bulking up, and would be better off following a 1950s training regime. This is not an outrageous suggestion, but if it is true, then we have to follow it to its logical conclusion. This would be that many fighters today are coming in too built up, and that it is hampering their performance.
I am also having a hard time with the idea that this is viable for Spinks, but not for Marciano. Spinks was a small light heavyweight you know. He was basically what we would today call a super middleweight, when he took the decision to move up!