First, welcome to the forum.
To narrow down the "date", you need to reference the engine assembly date. It is located on an extension (aka boss) on the block near the distributor. Pictures are from a 66 GT K Fastback built in San Jose in Oct 1965 with the engine build of August 23, 1965 (cast Aug 11, 65). The format is year, month, day, inspector/assembler - 5H11Z.
Jim