Managing Two Story Files in App Delegate

I've decided to avoid using auto-layout, so I'm trying to implement code instead so that my app is managing two different storyboards based on screen size.

I am following this tutorial: http://pinkstone.co.uk/how-to-load-a-different-storyboard-depending-on-screen-size-in-ios/

I am having trouble trying to translate Objective C code into Swift.

Here is the code I have in my AppDelegate:

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?

func grabStoryboard() -> UIStoryboard {
    var storyboard = UIStoryboard()
    var height = UIScreen.mainScreen().bounds.size.height

    if height == 480 {
        storyboard = UIStoryboard(name: "Main3.5", bundle: nil)
    } else {
        storyboard = UIStoryboard(name: "Main", bundle: nil)
    }
    return storyboard
}

func application(application: UIApplication!, didFinishLaunchingWithOptions launchOptions: NSDictionary!) -> Bool {
    // Override point for customization after application launch.   

    var storyboard: UIStoryboard = self.grabStoryboard()

    self.window?.rootViewController.storyboard.instantiateInitialViewController()
    self.window?.makeKeyAndVisible()

    return true
}

      

        
        
        
      

    

The app launches and I have no errors, however whether I run the app on a 3.5 "device or a 4" device, I just get a 4 "storyboard.

Where am I going wrong?