I think it's a definite possibility. But in a head-to-head fight, I think Foreman would brutalize Bonavena.
They each were only stopped by one man, Ali. But Bonavena was able to absorb his shots for 15, while Foreman succumbed in the 8th. This obviously doesn't automaticly put Oscar ahead, but it is something. Bonavena twice lasted the distance with Smokin Joe, and in pretty much every fight showed he could take a punch as his defense wasn't exactly Jack Johnsonish and got tagged often.
Both were very tough guys ... the difference was that Foreman was a much more dangerous fighter ... Oscar was very strong, Foreman was stronger ... Oscar hit hard, Foreman hit harder ... in his first career Foreman had stamiona issues. Oscar was not the world's greatest trainer but he showed better stamina than George ... both had very good chins ... I personally feel Foreman had the bigger heart as Oscar was , to me, a bit of a front runner ... A casr can be made that Oscar was more durable but Foreman much better and moe dangerous ...
In a head to head I think Foreman had the style to beat him by KO....Durable as far as past the 8th rd, I would would go with Ringo...Ringo was a solid guy but beatable and erratic and not always in top shape, he could last against a clubbing fighter but he had trouble with pin point punchers but Foreman did not fight that many punchers up to Frazier
When discussing Foreman you have to admit there were two different Foreman's ... career 1 and career 2 .... Career 2 George found confidence and inner calm and with it the ability to maximize strengths and abilities far better than the more physically gifted Foreman 1 ... Foreman 2 was much more mentally stronger ... That being said , Foreman 1 had a much better shot beating a prime Bonavena ... back to durability, Foreman 1 had stamina issues ... see Young, Jimmy as well ...
Foreman 2 handled the ring better, knew how to relax and pace himself, smarter and stronger mentally ...Foreman 1 was like a young bull
It might be something like the Chuvalo fight. Foreman by T.K.O. Bonavena takes a heavy beating but somehow remains standing. Oscar didn't have enough to hurt George.
Foreman was dropped for a count of 1 against Young,got up and chased him for the rest of the fight he was NOT LAID OUT.Bonavena was dropped by Ellis twice ,by Folley and by Ali 3 times
Bonavena dealt with Chuvalo, Ali, 25 rounds with Frazier, and Lyle.Foreman first time was a definitely stronger puncher, but tired out against Peralta.
If we're talking durability then there is no case. It's Bonavena, without question. Prime for prime he proved a lot more(durability-wise) in his career and was in many more rugged fights than GF. I don't believe that GF's chin would have survived 25 rounds of Joe Frazier slamming hooks into it. Lyle hurt GF and bounced him off the canvas many times. He couldn't budge Bonavena. People could talk about Oscar being floored by Ellis and Folley, etc. But I don't know that those same, quick and snappy shots wouldn't have floored and hurt GF too. Nat Fleischer called Bonavena the strongest HW he'd ever seen. I don't know that GF was stronger than Oscar. I just know that he was better at asserting his strength.