Project: Space Shooter - can't assign variable scoreText

Hello, I'm following the Space Shooter tutorial and keep running into a problem. I can't assign a variable to scoreText in the GameController script. First it seems that the tutorial is dated as I'm on Unity 4.60b20 on a Mac Pro and there isn't a GUI Text option under Hierarchy>Create. I created a UI>Text instead and try to drag and drop this into the scoreText field of the GameController script but Unity doesn't let me. This the error I get:

UnassignedReferenceException: The variable scoreText of GameController has not been assigned. You probably need to assign the scoreText variable of the GameController script in the inspector.

Here are the two scripts I'm using:

 using UnityEngine;
 using System.Collections;
 
 public class GameController : MonoBehaviour
 {
     public GameObject hazard;
     public Vector3 spawnValues;
     public int hazardCount;
     public float spawnWait;
     public float startWait;
     public float waveWait;
     
     public GUIText scoreText;
     private int score;
     
     void Start ()
     {
         score = 0;
         UpdateScore ();
         StartCoroutine (SpawnWaves ());
     }
     
     IEnumerator SpawnWaves ()
     {
         yield return new WaitForSeconds (startWait);
         while (true)
         {
             for (int i = 0; i < hazardCount; i++)
             {
                 Vector3 spawnPosition = new Vector3 (Random.Range (-spawnValues.x, spawnValues.x), spawnValues.y, spawnValues.z);
                 Quaternion spawnRotation = Quaternion.identity;
                 Instantiate (hazard, spawnPosition, spawnRotation);
                 yield return new WaitForSeconds (spawnWait);
             }
             yield return new WaitForSeconds (waveWait);
         }
     }
     
     public void AddScore (int newScoreValue)
     {
         score += newScoreValue;
         UpdateScore ();
     }
     
     void UpdateScore ()
     {
         scoreText.text = "Score: " + score;
     }
 }

And the second:

 using UnityEngine;
 using System.Collections;
 
 public class DestroyByContact : MonoBehaviour
 {
     public GameObject explosion;
     public GameObject playerExplosion;
     public int scoreValue;
     private GameController gameController;
     
     void Start ()
     {
         GameObject gameControllerObject = GameObject.FindWithTag ("GameController");
         if (gameControllerObject != null)
         {
             gameController = gameControllerObject.GetComponent <GameController>();
         }
         if (gameController == null)
         {
             Debug.Log ("Cannot find 'GameController' script");
         }
     }
     
     void OnTriggerEnter(Collider other) 
     {
         if (other.tag == "Boundary")
         {
             return;
         }
         Instantiate(explosion, transform.position, transform.rotation);
         if (other.tag == "Player")
         {
             Instantiate(playerExplosion, other.transform.position, other.transform.rotation);
         }
         gameController.AddScore (scoreValue);
         Destroy(other.gameObject);
         Destroy(gameObject);
     }
 }

Is there are way around this? I'm not a C# programmer and apologize at the noob question. Thank you.