help me identify my ls engine

[henry3rd]

Hey guys, I have been wanting to do this swap for a long time.Traded a mossberg shotgun for a 4.8 engine(I think) It has this number stamped into the block on the back 12567392 and the head gasket tab has a 4.8 on it.
I dont know what year it is.It has drive by wire and the connectors that go into the computer are blue and green.The guy I got it from took it in as trade for something and doesn't have a clue.It has the wiring harness but not the computer. I looked on lt1swap.com and the 2004 wiring diagram is pretty close but the c100 pinouts seem to be wrong and the wires from the big round connector that I assume is for an automatic trans all the wires are
right except for the gray wire which is the low reference goes to pin c1-47
which the 2004 wiring says is not used.I was thinking it was a 2002 to 2004
engine but I dont have the pin outs to tell.when I get a pcm for the harness
what year should I get? there is a big white sticker with a barcode on it on the back of the drivers side head does those numbers mean anything?
Thanks for the help i know I'll have a ton of questions as I go..