Interesting. Based on the autopsy it sounds to me like #4 was too tight due to the wrong bearing (undersize bearing in a standard bearing box) or there was insufficient oil supply to the #4 bearing. If the builder did indeed plastigauge all the bearings or the engine turned over at assembly, then I would guess an oil problem. 50 years ago I was working on one of the old babbit pounder 216 Chevys that have the oil dippers on the rods for rod lubrication. The engine was in the car and I got disoriented and got one dipper on backwards. The engine ran for about two minutes and locked up. The rod I had assembled incorrectly had fused itself to the crank and the rod was a pretty deep blue color. This sounds similar.