Factory installed spark plugs 1969 BB with cast iron heads.
 

Diggin for info on 1968 turned this up.
Pics 1- 2 are GM info announcing the new "ACniter" plug,
Pic 3 shows the 'performance" plugs came along much later.
Pic 4 shows one of the sets of boxes dated 1969 BB cast head plugs I have.

Pic 5 shows a
set of 68- earlier BB cast head plugs. Boxes dated 62 and 63 so maybe 409???
set of 1969 BB cast head plugs. Boxes dated 1969.
set of 1969- newer BB cast head plugs dated 1973. Note difference in box.

This is all I have on this so enjoy or ignore.

Differences between early and later ones.

Pic 1 shows actual 1969 examples

Pic 2 shows 1976 example.
Note knurling is same as 1969 but the later big top band is there.

Pic 3 shows 1969 and 1983.
Note knurling is different.

Same on the alloy head R43XL Acniters.

Something to look for

Pic 1 is 1969 dated. Note "NEW", no "GM" and "ACNITER" is bigger and "SPARK PLUGS" is smaller.

Pic 2 bottom is 1973 dated and note "GM" is added.
Also note "NEW" is gone, "ACNITER" is smaller and "SPARK PLUGS" is bigger.