+1 lake
If it was carbon, I would think the problem would not be localized to the exhaust skirt only , but would be all around the piston crown, also you would see much more sign of carbon about the rings.
Hard to say if the jug can be saved, if it is though the plating anywhere the jug is pretty much junk. Piston is junk for sure. I am not a big fan of honing plated jugs, the plating is very thin and ball hones have two problems. They can't get to the top of the bore and also they hit the edges of the ports hard and can cut through the plating in that area very fast.
I would say if the jug cleaned up nicely just a piston and set of rings, otherwise it neds a P&C.