I think Marciano stops him. Ruiz was able to land right hands against a Cruiserweight sized RJJ. If he can land multiple right hands on RJJ then so can Marciano. RJJ would probably make Marciano look silly for numerous rounds with the ridiculous speed advantage he has. But eventually Marciano would find RJJ's suspect chin with the right hand and then it's lights out.
Roy Jones at 190 pounds isn't the real Roy Jones. Carrying that much weight would slow him down, thus rendering him vulnerable to a contest-ending power shot from Rocky.
Jones overwhelms him and stops him, a lot earlier than most would imagine. Somewhat reminiscent of the Pazienza fight. An enormous gulf in talent and physical assets.
If Ezzard Charles and Archie Moore weren’t able to beat Marciano, I don’t think Roy Jones Jr. would have been able to do it either.
Marciano's vaunted right hand...the "Suzie Q"...vs Roy Jones' chin...Gee....Let me think about this for a while!!! Jones goes down like a cheap *****!
If 6-2, 78" reach Ruiz, who actually had decent feet, could hit Jones (and did he really that often?) then 5-9 67" reach Marciano, who had awful feet, could? Is that the logic you putting out there?
Roy at heavyweight was good but selective. His heavy weight win over Ruiz was more about speed and reflexes than destructive heavy weight power . Marciano might be one of the few men that wouldn't be discouraged by Roy's counters. Roy's speed advantage would most likely let him dominate early rounds. But the question is could Jones keep Marciano off him an entire fight ? 15 rounds remember.