My 1967 car had that extra engine tag on the drivers floor and there is a paint outline of that tag, no paint on the floor or the backside of the tag. Still had original carpet and interior.

I think it is the owners install them under the hood by the usual fender tag, I don’t think the factory did it that way. In the 80’s Looking at original paint, unrestored, and parted out cars I never saw one underhood, or the extra screw hole to mount it.

And IMO it looks REALLY stupid with it mounted under the hood.