I too just received a set of foams from the Darsts with the same problem. I left an email message with them but haven't heard anything back yet.
The sides of the repro foams are actually 1" wider than the original foams so I suspect a mistake has been made. They fit fine otherwise. I plan to cut the mouth opening back to the correct dimensions of 5 1/2" wide which should be easy enough but they will then have to be repainted since the foam is white. I'm concerned leaving it overhang will cause more problems with reflections than it solves since they have a crunchy surface from being painted.

