I'm taking Ingo's right hand against the southpaw. Mildenberger was a very good boxer but he could be hurt especially by right hands as Leotis Martin showed. Ingo was an even bigger puncher than Martin. I think the German has his moments but at some point Ingo is going to land a right hand.
Still remember people picking Mildenberger on the sole basis that he was a southpaw. Apparently being a southpaw wasn't enough to save Mildenberger from getting iced in one by Richardson, who promptly got iced himself by a washed-up Ingo next time out. So much for the magic left-handed advantage.
Ingemar proved conclusively that he was the best European heavyweight of his era. I consider Mildenberger to have been from that same era. Ingo would have nailed him by the 8th round.
I think after the Patterson fights he went downhill. Maybe he had a bit of concussion syndrome. I understand Brian London decked him at the end of their fight and actually he was saved by the bell otherwise would have been counted out. That version of Ingo I pick Mildenberger but the first Patterson fight Ingo I think catches Karl with Tooner.
I would probably favor Johannsson as he was a true world class fighter and Mildenberger didn’t exactly have the best chin. But it might not be easy. Mildenberger was a good boxer with sound defense and a southpaw stance .