The engine stamped code indicates it's a '57 or newer block. If I have the digits right, it translates to F= Flint MI manufacture, 10 = October, 31 = day of the month (a Halloween engine!), and J is the code for a '58 or later 235 engine originally in service in a truck, Thriftmaster 235 with 3-speed transmission. Since the engine serial number doesn't carry a year code (after '56), the best way to date the block is from the casting date code sort of behind and above the starter. You will see a series of raised digits staring with something like CON4, which is only the conveyor that he engine went down in the foundry - doesn't help - but the next 4 to 6 digits can be decoded to determine the engine casting date. This info comes from the '58 Chevy Master Parts Catalog.
Last edited by drdoug; Wed May 27 2020 12:55 AM.