Heres a few fights that could have happened cause they were both champions in the same time frame.

Salvador Sanchez vs. Eusebio Pedroza - This fight could have happened any time from 1980 to 1982 (Both held titles)
Carlos Ortiz vs. Mado Ramos - Don't know why they never fought they both fought the same opposition but never eachother
Jorge Castro vs. Julian Jackson - Both Middlweight champs what a thriller of a fight I think they would have put on
Terry Norris vs. Winky Wright - Makes you think doesn't it.....