[mr48chev]

One never knows what causes an engine like that to blow up if you aren't abusing it but I'd sure like to see the photos of the pieces after you pull it down/

In the past I've seen the results of:

Driving an engine that sat for years and had acid etched bearings have bearing failure.
Rod nuts back off the rod bolts.
Gobs of red silicone plugging up the oil pickup screen (My brother's truck that he bought off a car lot).
Poorly assembled engine due to the assembler not knowing what he was dong.

Dirt getting into the crankcase and bearings because the owner thought it was cool to run without an air filter. That is one reason that the Ford and Mopar guys used to say a V8 Chevy was only good for 35K miles in the 60's when a lot of guys thought it was great to drive around without an aircleaner for that drag car feeling.
the
Most folks here know my history but if you don't I spent 13 years teaching auto mechanics after several years of working in shops in Texas and Washington. I even got tabbed with keeping the generators running for the scout platoon of A troop First Squadron 9th Cav 1st Air Cav in 1968 when the platoon leader figured out that I had mechanical training.

Even though I have been away from the trade and teaching for several years guys still bring stuff to me to figure out what went wrong with it.

Now pull that engine apart and lets see what caused it to blow up.