As the above answer states, Johnny links Dally to the Southern gentlemen in terms of gallantry and courage. Dally may not share the Southern gentlemen's refinement of manners but Johnny, at least, is convinced that he is equally brave. Dally does show this, in a way, when he faces up to his own death at the end of the book; in fact he instigates his death at the hands of the cops because he doesn't want to live anymore after losing Johnny. The earlier invocation of the Southern gentlemen, depicted as riding fearlessly to their deaths in war, may be regarded as a form of foreshadowing in this respect.
Dally's sheer despair at the loss of Johnny illustrates what a strong bond the two shared. In fact, the friendship between them is one of the most poignant aspects of the book. On the face of it, they couldn't be more different: Dally is so wild and tough and violent, while Johnny is quiet, well-meaning and timid. But Johnny finds in Dally a kind of role model; he looks up to him and admires him, while Dally is fiercely protective of Johnny, 'the gang's pet'. Towards the end of the book Ponyboy suddenly realizes the depth of Dally's affection for Johnny:
Johnny was the only thing Dally had ever loved. And now Johnny was gone.