Marciano beat Moore, Charles. Qawi wouldn't have had a prayer, unless you think a mediocre fighter, at best, is going to stand in a slug with one of the top heavyweights. Holyfield at cruiser wouldn't beat Marciano; Conn fought Louis at 174, and Moorer's chin would let him down.
At this weight- 185- I think it really comes down to 2 guys, and, honestly, I'm suprised nobody mentioned it, as this would have to be one of the all-time dream, who would win if matches: Dempsey vs Marciano.
Though Dempsey did occasionally weigh 195-200, the majority of his fights were in the 185-190 range.