I had a big block on the dyno a few years back that ate a rod bearing and took out the whole engine during a dyno pull. The oil pressure was good the whole time but power started to drop and by the time we shut the engine off the rod bearing was torched and the engine was full of garbage. Never did figure out the issue but it had to be something off just a hair on that one cylinder since everything else looked good just like your engine. Could've been a slightly tighter bearing on that one hole or maybe some casting flash in the passage to that bearing or something along those lines.