lost all oil pressure but not flow

it's funny, I was just thinking about this thread, today. I just got my latest issue(September) of Hot Rod mag and they have a trouble-shooting story of a stroked RB engine, which has a reputation of breaking rocker arms, etc. It turns out the engine assembler mixed up two pistons, so that the eyebrows in the pistons were incorrectly matched to the particular valves in those cylinders. The intake valve(s) were colliding with the exhaust valve relief(s) in the pistons of two cylinders.