You can remove the piston by accessing it from the intake side. Remove the remaining plugs so you can rotate the crankshaft through the flywheel to have an easy access to the piston rod cap. Caution, you need to place the engine in full vertical. Stuff the space below the carbs with rags to prevent losing parts/bolts from falling in the space between the mid-leg.
Dismount the following:
Upper carb, intake adapter and V-block Reed. Using an extension and a 12 pt socket (1/4 inch), remove the two 1/4" bolts on the rod cap. Roller bearings will fall and make sure you recover them all. You will reuse them.
With the rod cap off, push out the piston and do further inspection of the cylinder.
Caution:
1. Note the orientation of the piston rod
2. Check the size of the piston and hopefully it's still the same as the rest. A number stamped on the piston head or crown indicates if it's still standard size of oversized. "1" indicates it's still standard. A shadow of "1" seems to be still readable.
3. If the gouging is light, you can try honing it using honing stones (Harbor Freight has them for like $30) and cutting oil. Otherwise, you will need to have it machined which means dismantling the head from the rest of the motor.
4. If you decide to use Wiseco piston (which is recommended and you can order one with the rings already installed) make sure you also order the wrist bearing kit. The new wrist is not pressed in but uses circ clips to lock in place.
5. The old wrist is pressed in and needs to be pressed out so you can re-use the rod.
6. Use your camera to take pics of everything you are not sure of.
Meltdown happens mostly due to lack of lubrication or cooling fluid. Did you have an overheat scenario? Or maybe failed to mix oil into the fuel? Or made the wrong ratio of oil and fuel? Or used the wrong type of oil?
There also seems to be too much gasket maker/sealant used on that head. In reality, you don't even need sealant to install the head gasket except for exceptional situation. But even then only a small film is needed. You might want to check the straightness of the head the block.
