With the glue now cured on the Antenna Support pieces, I unbolted and removed the Aluminum Channel pieces. That will be reinstalled again later.
I cut six pieces of 3mm styrene from scrap, each piece being be about 15mm x 30mm. I glued three together to form a 9mm thick styrene piece, then turned the head frame over and glued the two assemblies into place up under the Head Gun Inner Face. These pieces will later be tapped to screw down the top part of the head.