My monte carlo had an overheating issue, I couldn't figure it out so I stopped driving it, it sat for like 6 months.
Then when i started using it again it would overheat randomly.
Finally it got really bad and got white smoke, up til then I didn't think/was hoping it wasn't the head gasket.
So I decided to get to them.
It looks like it was leaking coolant into a cylinder that had started to misfire.

But I'm not really sure what the cylinder heads are supposed to look like, if it's corrosion or supposed to be a passageway. Either way I'm wondering if it's able to be saved.

 

I would bring them in for inspection. Appears that one bottom cylinder in first picture is the problem. You can clean them up and inspect for cracks. I usually use a wire wheel on a drill or grinder to remove all the scale.My eyesight isn't as good anymore so I use a magnifying glass and look carefully for crack between the valves. You can also check the head surface for warp with a straight edge. If you're unsure, best bet to bring in inspection and planning the head flat. Good luck