I have a 318 engine that came out of a Dodge M400 chassis (74 Winnebago RV). I think it's a 1973 block cast since i see 12-1-73 raised letters vertically along cylinder #3 between the coolant drain plug and freeze plug. The block number is a big mystery as I'm unable to find any information on what the driver side raised cast letters mean: "C 306|8". I have a similar engine from a 1969 Dodge M300 chassis (Winnebago D24) fitted with a similar HD truck application 318 engine with block raised letters "318-3" in the same location driver side between #5-7 cylinders.

I'm trying to confirm the block ID with no luck. Any advice is appreciated.