Most realistic 'best' Fighter Bruno could have beaten.

I'd say
Norton
Michael Spinks
Michael Moorer

Stretch possiblity s ,on a perfect night.
Ageing Foreman (if Frank doesn't tire in the later rounds)
Larry Holmes (the early 90s)

 

Not sure Spinks had the power to KO Frank.
The only two puncher s he faced were Cooney (washed up)
And Tyson (KO 1 )

 

He was out boxing George but Frank would be younger and a lot better jab himself.

 

I give Frank a 50 50 shot against Norton.
Ken could be Hurt early by big hitters, if Frank gets him in early then he's a great chance.

 

Comparable id say.
And Cooney was in no great shape really by the time he fought Spinks

 

But he had a fragile Chin

 

But never really stopped early apart from Tyson.