Dave Van Buren sent in these two photos from Trenton Engine’s archives. The first shows final inspection of engine blocks for Department 72 Main, which made the low-deck B-engine blocks—the 361, 383, and later 400. The bore sizes were painted onto the blocks because there were variations in the diameter of both blocks and pistons (shown below, newly minted); later, pistons were chosen to match the closest-size cylinders. After the final inspection shown above, blocks were loaded onto the assembly line. The slant six line was similar.
Many more photos from Trenton Engine and other plants are at motales’ plant pages.