I want to make a list of the most unorthodox, ugly and awkwardly effective fighters. Boxers that require you to bring up their attributes/achievements. The kind of guys you'd have a hard time validating off of the eye test alone. I'm not counting the Ali's, Emmanuel Augustus', and Pryor's of the world. They still made their weird look good. The cutoff is whether you think they could win a title or not. So far I have: Michael Spinks Carlos Monzon Vitali Klitschko Saul Mamby Bazooka Limon Max Baer George Foreman Stanley Ketchel Teddy Yarosz Gene Fullmer Tyson Fury Emanuel Navarrete Ossie Occasio Rocky Marciano Carmen Basilio Manuel Medina Luis Lazarte Khaosai Galaxy Shoji Oguma Keep em coming!
It depends whether you mean fighters that aren't aesthetically pleasing to watch or don't look effective, despite obviously being so. I don't think Mickey Walker or Emile Griffiths are stylists, but you can easily tell by watching them how effective they are. Neither Stanley Ketchel nor Teddy Yarosz (for very different reasons), look like they've top tier effective boxers at first glance, but they certainly were.
Frans Botha... he wasn't a great boxer, of course, but looking at him, it was hard to imagine he could be a contender. Not very tall, not very fast, didn't look technically advanced, had rather average cardio, and an average jaw... yet he was a pretty strong heavyweight for a while. His compatriot Corrie Sanders also didn't look like a hero, with his paunch and ultra-stiff stance, but he had very fast hands.
Not familiar with Corbet or Fitzsimmons or that era of boxing to find anything that stands out. Moreso the latter than the former, but a bit of both is needed.