Well to tell you the truth, that doesn't particularly look like a motor that died from overheating. Mostly if they overheat they seize the piston in the bore, but not smash the piston to bits like that. Does the bore have signs of it locking up, like aluminum stuck to the walls of ? And which bit was seized ? It wouldn't have been that piston/bore I'd bet. I'd assume that it was just an old worn out motor that was making noises and eventually got a big rev and broke the side of it's piston because of the way it was rattling around in there. And the top ends often smell like overheated oil.. I'd inspect everything for the usual signs of wear and damage and then go ahead and overhaul it. I've done heaps of motors that looked like that, and worse, and they all rebuilt just fine.

It sounds like a broken ring, but, if there's really heaps of smoke.. and I mean if it's just pouring out, and white not blue tinged.. change the oil. I've seen motors with the wrong sort of oil in them that run good, but just streamed white smoke out the back.. the whiteness of the smoke being the clue. In those cases the motors had just had an oil change and it was easy to guess what it was. Changed the oil and they came right. The noise could be caused by the oil detonating. Doh... I really must start taking better notice of the dates. Probably worth mentioning (now we are here), that in one of those cases, and suspected in the other, it was chain bar oil that had been put in by mistake..