how do you tell the year of the engine

[GMC70c20]

I have a lq4 that I bought fomr a junk yard a couple years ago, when I got it I was told it was out of a 2006 van. I need to know how do you tell the year of the engine? is there a casting number somewhere on the block if so where is it? I know its a genIII block, it has the cps in the back of the engine and has 317 heads on it. It also had a dead head injection system on it. I was under the impresion they when to genIIII in 2006, but that was the suposed year of this engine I'm confused.