Are the numbers on these AC brackets date codes?

 

Yes. 336 is the 336th day of the year, so Dec 2 (or Dec 1 in a leap year). 2 is Jan 2.

 

I tried my best to learn something from this thread. I'll agree 336 would be a likely number for the 336th day of a calendar year. If only I could find the number "336" located in one of the images I might be able to learn something here. WTF are you talking about, Joe?

 

The little plates retained with screws to the casting core is the date code

 

Holy Guacamole. I stared at those images & lost my mind. Wow, got it. Thanks!

 

Thanks Joe...what would the year be, and how do you tell?

 

You would tell by the model year of the car they came off of, unfortunately. 391366 was used on all 1966-72 Cutlii with A/C and all 1966-78 Toronados with A/C, for example.

 

So each year didn't have a specific code, it was just the Julian date code?

 

Correct!
It could be any year.

 

At the time GM used several different methods for date coding. Some methods do use use one, and some use two digits, to signal the year of the part. In addition, some indicate information like shift and time of manufacture.

 

Since we're on the topic, how were those (Julian) date codes affixed to a casting mold, and what was their material(s) of construction?

 

I don't have first-hand knowledge, but it appears that these were simply stamped straps of thin sheet metal that were screwed to the mold core.