A battleship vs a battle cruiser. Foster, if he feels really threatened, doesn't mess around, and takes Hearns out quickly. Foster inside 4 rounds.
You would think Foster, but Hearns is fast and you wonder how Hearns punch on Foster's chin would do. My guess is who lands first wins.
Hearns would have no physical advantages in this matchup except hand speed. Hearns best bet is to move and box. But once he slows down a bit, Bob takes him apart. If Hearns trades, Bob takes him and takes him out early. If Hearns boxes, Bob takes him out late.
what is in Hearns favor is beating better guys. But Foster has the advantage, but Foster had a suspect chin himself, so who knows. And if Foster hit most guys at 175 they would go regardless of chin, so on that alone I give Hearns a chance on his speed.