Block heater for Grand L-4240

[dfixit1]

From the picture of the block with removed plug, what is the aluminum above & below the slot, is that just to keep the plug from going in too far? What happens if one of those gets drilled? I know the cylinder wall is in the back, I'm just talking about what is seen in the picture.

Not Aluminum, part of the cast block. Looks clean from coolant.
from another reply in this post....
“All the soft plug holes in Tier 4, common rail blocks are shaped this way.”