in the 70s if we were to rank top 3 hardest punchers

I've pointed out this one. Young Foreman had a decent chin, but not the iron chin of Old Foreman.

Then again, this isn't unprecedented -- Muhammad Ali was the same. When young, Ali could be knocked down, hurt badly, etc. Once he got past the FOTC, he became one of the must durable fighters out there.

 

Reuben Olivares
Alexis Aguello
George Foreman

 

Foreman
Shavers
Lyle

 

Frazier was no ko puncher.
He perhaps scored ONE knockdown with his right hand. That’s it. A record.

What top opponents did he ever ko for a ten count? Machen and Foster?

Attrition puncher.