Bonavena at his best was a top five, world class Heavyweight; Bruno never beat anyone that good (peak Oscar). Bonavena would probably have to concede the early rounds, but in the end you know the score. Bruno to be TKO'd late, in a brave defeat.
Bruno and Bonevena never had the big wins. People keep talking about Frank's deficiencies, but I think he could have beaten a lot of the good 70's heavyweights. Bonevena was very good, but he took a lot of shots. Bruno was a very big hitter, and taking punishment from a guy who way 35 pounds more than you is not something a recipe for success. Frank's muscular body always tired late in the fight, but I think the punishment he dealt out would have worn Oscar down. Frank by decision in a 10 or 12 round fight. I would favor Ringo in a 15 round fight.