The date code is actually below the
oil filter adapter mounting pad. On 63 and earlier blocks it is above it as jwoodard stated. But a C6 casting will have it below. It's on a small angled part of the block and it's a number/letter/number sequence. The first number is the year ending, the next letter is the month cast A-M skipping the letter "I" so A for Jan, B for Feb and so on. Dont' forget to skip "I". LOL. The last number or numbers is the day of the month the block was cast. Ex 6J20 = 66/Sept/20th. The letter "I" was skipped as it could easily be confused for a number 1.
G.