I've got a brand new 2004 ls6 block and wondering if it should have a coolant plug here.....directly above the oil galley pressed in plug...

 

What's wrong with the one in your hand?

 

that's an oil galley plug, ain't it?

 

The problem is: Whether it needs to go in there or stay in his hand and then be transported to the work bench. He is asking if there needs to be one in there.

 

Not the oil galley plug. The bolt hole directly above the oil galley plug that is pressed in...

 

The left hole is supply IN from the oil pump, 2nd hole is the plug for the casting hole and the 3rd threaded plug stays also.

Here is the lubrication schematic, I hope this helps:

There are slight variations in the other Gen 3 blocks, but nothing substantial like a coolant block plug missing.
This diagram is only for 2004.