Where are the "Knock Sensors" located on the 2001 Vortec 4.8L

For anyone who might have a question about the Knock Sensors, they are under the intake manifold. To replace them the manifold has to be removed in order to get to them. And why they are numbered #1 and #2 can only mean one thing...the front one is 1 and the back one is 2. They are not left or right...only front and back. This came from a Chevrolet mechanic...not me.

Never mind.