You really want to relate the date to the build date of the car, not the engine. Assuming this is a U.S. built car, you probably don't know exactly when it was built. The code at the top of your cowl tag (body build date) will give you an idea. It'll be something like 03D (March - 4th week). There are exceptions, but usually the production date of the car was soon after this. In Canada, GM documentation tells us exactly when cars were built. We find that parts dates vary, but generally are 1-3 months prior. As an example, my L79 was built Nov 26/65 and the carb was 3rd week of August/65.
Bob