I have a 2004 GTO, without having to crawl up under my car in the Hot Houston weather, can anyone take a stab and tell me with my specs, what engine block I more than likely have?
LS1 or the LS6?

Build Date is November 2003

I have read some information that leads me to believe its a LS6 Block.
See Attached:

 

You probably have the LS6 block. I don't believe GM used the LS1 block after 03.

GTO is a bit different tho since it's Aussie and shares a lot with the F-Body.

 

cant you tell from the ls6 pcv location? I know I converted my LS1 pcv routing that went in to the valve cover to the ls6 style that went into the valley cover, I'm just curious and not stating look at your pcv routing

 

04 everything got the 1168 block, so yes, you have an LS6 block

 

The LS6 has windows underneath the cylinders, whereas the LS1 block is gun drilled all the way through under the cam tunnel. You should be able to Google pictures for a visual reference.

 

I checked its a LS6 block.

 

Yup, LS6 block with LS1 top end (well except for the intake manifold which is LS6)