Before even thinking of buying a head I would do some very close inspection on the rest of the engine. As I said above in message 212 I would be very worried about this engine! Those are about the worst cracks I have ever seen in a head. If someone keep running it with coolant low due to the cracks there is no telling how much other damage there might be. Scored cylinders and scuffed up pistons might be just the start of things. I would be worried about things like cracked block, bad main and rod bearings, scored crank and bad cam bearings, just to name a few.
I doubt this damage you have already found happened in the last couple minutes it ran before being parked! I believe I have said it before, I'd put out some feelers to try to source a running take out engine. That would still involve a bit of risk but the only other option I would feel comfortable with from what I have seen is a total tear down and careful cleaning of each and every part with a close examination of all components.
Anything less would, in my opinion, just be asking for something to bit you hard in the pocketbook five minutes after it does fire up for the first time. Either that or hire an old retired Cat mechanic to come out and evaluate it as it set right now. If he doesn't have grey hair find someone else. This is not a job for someone who's first step in fixing a machine involves finding the plug-in-port for his laptop