In a case like this, it’s a nuke from orbit sort of thing.
If I were tackling this, I would only save the actual content (copy, images) itself and start fully from scratch.
What tools you use is up to you. Have you used a grid system before? If so, maybe stick with that one… if you’re open to alternatives, there are plenty like Bootstrap and Foundation to choose from.
If you’re feeling really saucy, rolling up Susy is fantastic once you get past the learning curve. (Especially if you know a task runner like Grunt or Gulp)
I think trying to save any code would waste more time than it would save.