In a matchup between a very good lightheavyweight and a great one---I will take the great one. Spinks by late stoppage or UD.
It would be a competitive (but, not necessarily close) fight. ... Up until Spinks takes him out late in the fight.
Dariusz gets well beaten without being disgraced. He showed he could overcome a speed disadvantage and beat a slicker fighter in Hill, but the difference is that Spinks doesn't just box in reverse, and even if you get past his jab he's got some underrated punch power in close (ask Marvin Johnson about that!). With Dariusz's total lack of an inside game and vulnerability to uppercuts, if Spinks is on his A-game and takes Dariusz's legs from him for enough rounds I could see him walking him on to a similar short hook or uppercut inside and closing the show in the last couple of rounds. Generally, though, I'd imagine that Dariusz's durability and long-fight fitness takes him the full distance where he loses a pretty wide decision, something like 117-111 over twelve or 146-139 over fifteen. Spinks just has too many angles and too much class to lose to Dariusz in my opinion. One was a good Light-Heavyweight champion who'd be a respected operator in any era, the other is one of the all-time great Light-Heavyweight champions who'd be an outstanding operator in any era.
Spinks KO9 His jab is better and quicker than Shevksi's imo, he'd start slow but still prove that he has the better left, after 4/5 rounds he'd be outjabbing and counter jabbing Darius at will and then would mix in some straight rights and left hooks. Darius's robotic stance would allow Spinks to land quite easily on him and start to ware him down before landing a clean blow with enough power to take him out. Shevski wins the early rounds, Spinks takes the mid rounds and it starts to get one sided
I imagine people would favour Jones over Spinks. Possibly Foster and Moore. Loughran, Conn and Tunney all give him issues but imo all of the above ultimately lose. Ezzard Charles and Harry Greb are the only 2 I'd favour with any degree of certainty.
Spinks by decision over Michalczewski. I don't think Spinks would have beaten Roy Jones though. Jones' style was wrong for him. Jones would likely pop him with quick shots all night and stay out of harm's way.
Yeah, I think this is the best breakdown actually. DM would have success early, as Spinks was one of the all time slow starters. But Spinks would warm up, and methodically break him down. I think the Jinx would end matters circa 9, as you said.