REALLY BIG HELMET!!!
I added a length of half round plastic strip around the opening and sprayed on primer/filler.
I did some test fitting and decided that the Helmet & Fink Head were too large.
I laid 2 strips of 1/4" masking tape on the helmet, one from front to back, the other from side to side. I traced the 2 lines, removed the tape and cut the 2 pieces out of the helmet.
Then I glued the 4 sections back together.
This should be the perfect size...