This is the piston from the 1988 KTM 500mx I picked up (see the previous post).
You can see the giant gouge that was created as coolant flooded into the cylinder from the blown head gasket. When metal changes temperatures that quickly there’s really no predicting how severe the damage is going to be.
The cylinder has a matching scare on it but is otherwise in good condition.
Unfortunately these pistons are a bit hard to come by these days. Some custom piston houses do limited runs from time to time. There are also a few remaining NOS pistons on dealer shelves and the guys over at KTMTalk.com bump into them from time to time while fishing through bins like old vinyl.