Like Fitzsimmons? There hasn't been any in the last 100 years, bar Fitzsimmons a himself and Sam Langford. There the only two, it's just a coincidence that only 20 years separated them. There's been alot of hard punchers that are CWs, Haye and Gassiev jumping to mind first, that would've been LHWs in the 50s. Wilder has been routinely KOing HWs much heavier than him. There has been some incredibly hard punchers pfp, McClellan, Jackson, Hearns ect. These guys where near enough the same size at Langford and Fitzsimmons but the sport has evolved financially, meaning there's livable money of not fighting as a Heavyweight.
Hard to say but I've a feeling this isn't going to last 5 round s .I'll say Bob has to pick himself up , several times and comes back to score a vicious ko over Rahman.
Let me see Fitsimmons a 5'11 150 to 160 pound guy who turned pro in the 1890's and had primitive skills were Hasim Rahman a 6'2 230 pound guy who had modern skills. Rahman by first round murder. But hey the adult diaper wearing seniles of this Classic section will say but Bob Fitzsimmons was considered extremely skilled for 1890's to early 1900's standards so that must mean he could beat modern fighter who was much bigger than him.