If everything is mounted correct and most the air is out, try giving the clutch one pump for pressure to see if that lets it go into gear, like you are pumping brakes. I would avoid gridding--- can chip teeth. If that does not work try a ½ inch longer rod, but there should be enough thread adjustment. The older Spitfires did not have threads on the rod and they had a little piece to put onto the rod until the clutch wore in some.
steve