Provided Oscar does n't hurt him badly enough to force a stoppage,it's feasible that Leon could outwork Bonavena over 15 rounds. A big IF though.
The Ali spinks beat was one of the weakest lineal champions ever. Very lethargic, coasted many rounds, had almost zero steam on his punches, legs were gone, head movement gone, etc. He was champion in name only. Spinks best assets were his high workrate and scrappiness. Lacked in a lot of basic fundamentals and wasn't a very strong hitter or particularly fast. He'd be coming forward and throwing a lot. Oscar was no technician, but he comparatively looked way better against a much younger and still competent Ali. He also beat rugged come forward guys like Chuvalo who I wouldn't be confident betting against if he fought spinks either. I wanna say it goes the distance in a very thrilling phone booth war. Oscar might produce a knockdown and takes a close decision due to slightly better ring IQ and being the stronger and harder hitting guy with a decent jab.
Bonavena crushes him .. Leon was a blown up cruiserweight that caught a near shot, undertrained Ali perfect and never beat another top contender unless you consider Mercardo (gatekeeper) a class win ... Oscar was a skillful brute that went to war w Frazier, Ali, Patterson, Chuvalo and many others .. not a good fight for Leon ..
Ringo Bonavena was vastly superior to Scott LeDoux, and Scott roughed up and stifled Leon in their bout...and held him to a draw. Oscar would treat Leon far worse. A decision win over Spinks...maybe decking him a few times for good measure. Leon wasn't much bigger than Joe Frazier...and Oscar knew how to fight short, smaller heavyweights, ...decked and gave them all they could handle...even if he didn't always win. Bonavena would be waaay too tough, strong and awkward for Neon Leon.
I could see Oscar Ringo Bonavena insulting Leon Spinks by asking him in broken English, Why You No Have Teeth? It would be in the same manner that Oscar angered Muhammad Ali by asking Ali, Why You No Go In Army?, Chicken Clay, Peep, Peep, Peep. Leon feeling insulted would go right after Ringo, attempting to keep him on the ropes, but soon he gets mauled by Bonavena, only to suffer a KO 4 after being heavily bombarded by extensive body blows that bring down his guard, making him vulnerable to a hard right hand that ends it for the night.
OSCAR NEVER STOPPED AN OPPONENT IN THE TOP TEN, BUT HE'S LIKE A GODSEND ON BOXING 24, I'LL GO WITH Neon Deon, if we're going by 2/15/78. Whomever wins a fite like this one is the man who's going to throw the most punches I see the Spinks Jinx in this one, especially if Oscar backs up on the ropes like he did vs Joe Frazier, Oscar was shrewd and knew his limitations and of course dangerous, Just did not match up well with the top.
Bonavena was tough and strong, and gave the best of them hell, but that was about it. Bonavena did have the hunger Spinks did to win I think (obviously it wasn't enough to give Spinks a great career), but I think Spinks outslugs him anyway.