Im curious, (if you don't mind the sharing) what was used to cut the hole in the back? Will you use the dropout piece to go back? I'm trying to decide on how to do this on mine, and haven't settled on a final plan yet.
Incidentally, I have Guild Starfire II BA-1407, a 1967. I'm doing the Alembic mods to a nearly identical Newark Street reissue though.