Alternatively you could use a US-100 instead of HC SR04:
http://forum.arduino.cc/index.php?topic=458557.msg3191753#msg3191753
It can operate with 5V as well as with 3.3V logic from Due.
You have to spend 2.37$ instead of 0.81$ for HC SR04 on aliexpress.com.
Hermann.
I superglued 3 together for my Due (with motorshield v2):
And they work well.