What particularly durable light heavyweights did Spinks KO. I know he stopped some guys there but I was unaware of any exceptionally durable guys stopped by him.
Willie "The Bull" Taylor was known for having a granite chin at the time he faced off with Spinks, one that John Conteh infamously broke his right hand on in 1975. The Jinx practiced his power punching on Taylor for over seven rounds, to the point where his hands were hurting badly. Finally, the referee stepped in to stop it, just as Taylor was cranking up another wild roundhouse left. (That was Spink's warmup for Marvin Johnson.)
Mustafa Hamsho, Hagler put over fiftysomething stiches in his face & he kept coming, only the referee showed enough mercy to stop it. And noone else came close to stopping him. Very tough fighter.
I know that unstoppable doesn't necessarily mean undroppable but McCallum's been down twice -against Tiozzo and then against Herol Graham, 4th round. That hurts his case. I can't mention him in the same page as Hagler.
I'm fairly sure it was RJJ that dropped McCallum (in the 10th I think) and not Herol Graham, who punched nowhere near hard enough to drop someone of McCallum's chin calibre.