As for the technique of stabilizing FT-243s, it is attributed to Bliley, although I wouldn't doubt that others discovered it as well because it was essentially discovered by accident.  Bliley used HF etching for the final small move to the design frequency.  That etch accomplished something else that was very beneficial.  It got rid of the loosely attached bits of silicon oxide that were mechanically trapped in the surface.  As the crystals were used in the field the vibration dislodged that material, which reduced the mass and caused the frequency to rise out of spec.  Bliley was forced by the govt to surrender their Intellectual Property to other makers.

I have done a lot of surplus crystal etching using a buffered HF solution (don't use straight HF for God's sake).  If folks are interested I could write down my learnings.  I will share now that a quick dip in the solution will "clean" a blank far better than alcohol can because the aforementioned silicon oxide fragments clinging to the surface are easily removed by the etch while the well ordered crystal structure is resistant to the etch and doesn't reduce during the dip.  The freq typically goes up 100Hz as the mass is removed.  Q improves as well.

Dennis AE6C