alreet mark, hows it going? that looks a canny one! whats that stuck on the exhaust side of the piston? looks like something has been sucked in, or a ring has spun, snagged in the exhaust port, and forced the piston crown up. its been running hot as well by the looks of it.
At least there is no sign of pinking That certainly is a bad one. Barrel ok?
In the first picture before the crown was cleaned it looks like its running really very lean. The plug must have been grey.