Ooooo, i'm loving that Dennis Andries answer, though he kept learning. I'll roll with that, Dennis Andries.
Hmm.. depends on what you consider talent. People with little boxing talent who made the most out of what they had with heart and determination would be: Barkley, Pazienza, Mancini, and Gatti. There's countless others but these guys actually won titles.
Mayorga in his prime had good hand speed, concussive power, a granite chin, and heart that was unmatched in boxing. I'd go with Carlos Baldomir.
Jim Watt, maybe? Only modestly talented, but very tough and cagey, and consistently found ways to pull out fights. Thwarted two heavily hyped challengers in Howard Davis and Sean O'Grady. How about Eric Lucas?