The Outsiders/WMG

Johnny is an Alternate Universe interpretation of Johnny the Homicidal Maniac.
Think about it. Same name, both killers, both orphans, both need very little to be pushed over the edge. Thus, if Johnny of The Outsiders was raised elsewhere without the Greasers, he'd become Johnny the Homicidal Maniac. Hey, it's an Epileptic Tree, but still.
 * Dallas is Johnny the Homicidal Maniac. He  and renamed himself after his friend.
 * Our Johnny isn't an orphan, though, merely a kid who doesn't spend a lot of time at home because his parents are neglectful at their best and abusive at their worst. And it can be argued that it takes a lot to push Johnny over the edge--nearly beating him to death and then almost drowning his best friend, to be exact.

Darry orchestrated everything.
Think about it. The Curtis kids are all smart in their own ways (Ponyboy is a literary genius, Soda is excellent with cars and women.) After Ponyboy ran away, Darry probably called up his old friends-turned-socs to help look for him and put the fear of God in him, teach him a lesson of some sort. Unfortunately, Johnny ruined his plans. That's why he had to die...

OR

Darry orchestrated even further: Bob faked his death, and when Ponyboy and Johnny went on the run, Johnny was feeding the gang info on their location. The fire was started on purpose (for some reason, DON'T QUESTION DARRY'S LOGIC), but Johnny was a casualty.

Nevertheless, all is well in the end.
 * Alternatively, Darry wanted Pony to have better friends, ones that stay in school and don't drink or get him in Rumbles. But their gang was also their family. So Darry had to arrange some "accidents."
 * So... Darry's part of the Mafia, then?
 * With this level of intelligence and planning, he's the head of the Mafia