Mystery engine

Just for an example: I looked at an engine the other day and on front of block was 9W 360 ?T 6419 0???. Could barely read it, and not all of it, but 6419 put the assembly date of engine near to the vehicle assembly date (prior to it as well). I interpreted that number to mean 1979, Windsor, Truck, 6419= About 20 Feb. 1979. Last four numbers were number of engine built that day. Special built engine so very low volume, only 30-40 (daily average) of this engine maintained on hand in assembly plant engine inventory.
I use white grease pencil or chalk to wipe across numbers after cleaning with brush. Then wipe with rag in one direction. Numbers show up better for me that way.