Factory installed spark plugs 1968 BB cast iron heads.

[jeffschevelle]

If you can't get to the flap with the date on it (or it is gone), some manufacturing date indicators to keep in mind are:

(A) The presence of the Registered Trademark symbol (R in a circle) beside the AC logo is later than the ones without that symbol. But keep in mind that they did not always put it beside the AC on all sides of the box so you need to look at all sides to see if it is on any of them. And

(B) The presence of the GM logo in the square box is later than the ones without the GM logo.

Happy hunting!