The pads were masked with a piece of tape as the suffix had to be readable at the entry to the shipping dock conveyor system so the engine could be routed to the correct spot along the dock for racking and rail car loading; the suffix code was scrawled on the side of the block (upside-down) in grease pencil at the first (air-gage) station on the engine assembly line, but that wasn't visible after the paint booth.
The engine plant stamp was done on big-blocks BEFORE the heads went on, and AFTER the heads went on on small-blocks.
