It Is from the rough stage of machining of the block for lifter holes for clearance. so final tooling to bore and finish valve train lifter bores ..
Retired form Chrysler Trenton Engine plant ..Seen a lot of them..
So was this something done after a certain year? Or just by a certain block plant? I've never seen it on a factory built engine. The engine Chris is talking about was as built when new, Bearings were dated 2-72 so it is a virgin engine.
