If had to guess, I would say the top piston did seize. It doesn't look too bad but is stuffed. Cracks in the ports are easily welded up but I think they will have to be re-nikasilled if welded.

I am no expert on this but if it was me I would weld the crack(s), have both cylinders recoated and do a full top end rebuild.

But thats just me.

Andy

Bandit7