Just to close out the discussion on the plastic cups (OBTW - I agree with everything said above)….
The little cup were a Ford update published as a Technical Service Bulletin on 08-03-73.
As Doug mentioned, "King" had some NOS ones. I think the originals are a yellow plastic color.
You can also get similar PPG plastic cups from good Body and Paint shops. They fit right into the existing factory holes (and aren't discolored like 45 year old ones that have been installed in a car are).