Sandy Saddler supoosedly converted from the southpaw stance, hence his penchant for extended read hand. Howard Cosell notes before the Ellis-Bonavena bout that Oscar was a zurdo before converting (which perhaps added to his awkward style) and another Oscar, this time the Golden Boy, was originally a lefty. What are some other notable examples?
Tony DeMarco and Rodolfo Martinez were both converted southpaws. In a strange turn of events, the southpaw Ayub Kalule was actually right-handed but learned to box from his brother who was a southpaw. Not knowing any better, Kalule fought like he was shown, thus a southpaw was born.
Although i dont think he ever fought out of a southpaw stance, Miguel Cotto's dominant side was his left, yet he fought out of an orthodox stance.
He actually did go back and forth in some fights (notably against Zab Judah). Winky Wright is a right handed southpaw fighter (hence why that jab and right hook were so crisp)