Yep! It happens.nnnnnnooooooooooooooooooo!!!
What a bummer. New motor sounds pretty rad though
this ^^ is what I thought too ... can you extract what's left of the bolts from the number two main webbing? maybe a closer inspection will reveal something ....I don't get it either. The only conclusion I came to was the bolts on the number 2 main cap were either over torqued or under torqued from the factory. One good thing about this failure is the head usually survives. The last time it happened to me, the only reusable parts from the bottom end was 3 pistons and 3 rods.
If I were in your place right now, I would find a low mileage short block, do the intermediate bearings and some arp hardware for the mains and rods and call her good.
In vanagons I know of one broken crank and two with main bearing issues not as extreme as this but probably would have been if run longer.your truck is grocery bag in the wind compared to a syncro westy, or a plain westy for that matter.... tons of those running around with modded tdi mills on stock lowers with zero issues....