I saw one like that here a few years back, coolant header tank had split round the seam where they often do, and the driver carried on driving it more or less till it seized completely ("there was a funny smell coming out of the heater so we stopped"...).
All the plastic fittings on the engine block were melted. It was filled up with coolant and started with the header tank cap off, it "evacuated" the entire cooling system (through the header tank cap) in about three or four seconds which caused a bit of a scattering match among the assembled audience (spectacular though), and it sounded horrific - just huge metallic clanking noises a bit like somebody belting an anvil with a sledgehammer on every piston stroke. It went in the bin!
The solder in the rad hadn't melted though - what is the melting temp of solder?! maybe this one had been even hotter, though I can't quite see how it could melt something on the rad? must have been hot combustion gases going through the rad or something as even if the engine block was red hot the radiated heat wouldn't be enough to melt solder, the vehicle would catch fire first! If it was combustion gases escaping into the rad to that extent I'd say it will be somewhat bladdered....
From cooked ones I've seen in the ten years I've been working around the vehicles I expect the head will be bent like a banana (the alloy heads are the first thing to go when they get too hot) and if its been that hot the pistons will probably have picked up in the bores too.
What was the cause of the bang Les - oil loss or coolant loss?
Nothing that five grand won't fix