RE: An oddd request
Just for nomenclature.....
What you have shown there are the piston, sleeve/liner and the head button.
The clamp is the finned section that bolts on to retain the head button and sleeve assembly.
The coloring is generally ok. Nothing real unusual, but darker carbon deposits happen when running the engine a little rich, but it getting hot (over-propped or pipe too short typically).
What concerns me are apparent pits on the top surface of the piston --- it looks like it ate something... ?? Might just be artifacts from the photo.
If everything is in decent shape, and the glow plug threads are not stripped (as you first though) put it back together and run it. I would suggest just tossing a 10x6 or 9x7 on it for a few runs. Make sure to double check the head clamp bolts after the first run.. jsut to ensure they are still snug.
Bob