Tom, This was my quick and dirty, for proof of concept... It worked, If I were to make it again I would make it a bit longer, somewhere between 6 or 8 inches.
This one is 2 3/8th by 3 3/4's because it's the piece of wood (maple) I had at the time.
As I remember...
Turn between centers, tenon each end.
Grab tenon, drill to fit end of gun drill.
Reverse, drill and tap for air fitting (1/4 NPT)
Soak threads and end grain w/ thin CA, retap
Mark, drill and install threaded inserts.
Teflon tape, ball valve and air fitting.
Needed some light scraping to fit drill, Threaded inserts had to be filed/sanded flush. Thought of putting a gasket in the bottom but don't feel it's needed, a bit of air leaks by, but not enough to worry about.
Hope this gives you some ideas.
cc
Edit... my NPT was off, thanks Al, for the catch...