The harness should still be similar, differences would be where the connections are for the alternator, the connections for the trans if the engine came with a 4L80E, the injectors use a different connector but should be in the same place. And they didn't go to the DOD in 04' so that makes it a bit easier. What exactly are you trying to figure out? Let me look through some of my old pics, I used a 5.3 for a build in my 69' Pontiac a long time ago, maybe I have some pics of the wiring from that.