I've looked through the parts catalog and do not see the 2 1/2" round inserts listed. One is located directly in the middle of the play field labeled The Sun", and the other near the pop bumpers labeled "Increase Energy Value".
Both measure 2 1/2". The inserts are shown on page 7-6B, but these aren't listed.
Also the one near the pops is located under the mylar. What's the trick to removing mylar without ripping off paint?