Yes they installed them on 67s but its best not to mix years or even assembly plants so lets focus on only 68's in this thread.
Not sure where your car was built (might want to add that to your signature
but it would likely help the discussion
But if you look at the pictures posted in the unrestored picture threads and similar cars you will find examples with the seal. How they were attached will likely match up with when and where your car was built
If you provide more details than we can look further into the subject and confirm additional details and or we can investigate if your radiator support has been changed at some point in the cars history