Intake casting number

[Camaro Billy]

Here some shots of my engine pad and the casting date of my intake manifold. My question is did the skip the letter "I" on intake manifold castings ?
If so the date is perfect.If not my manifold was cast after my engine was built. My car is an 11D '68 build and has the large type trim tag. I have seen 11D both large and small type tags, so guess that means my car was a later 11D build.

[Jerry@CHP]

GM used the letter "I" on engine blocks.

Jerry

[Camaro Billy]

So that makes the intake about 2 weeks to late for my engine, correct ?

Billy

[Jonesy]

They used the letter "I" for casting date on intakes. "I" was Sept so your intake is dated Dec 2, 1968