The P-38M was developed as a night fighter.  It had an AN/APS-4 AI radar pod under its nose and was painted gloss black.  The war ended before the M's saw any action.
The Droop Snoot conversion kit converted a P-38J to a level bomber by replacing the armament in the nose with a bombardier compartment - complete with a Norden bombsight.  The AAF ordered 100 Droop Snoot conversion kits, although its not known how many P-38J's were actually converted.
The Droop Snoot did see action.  The first mission was by the 20th Fighter Group on April 10, 1944 against Gutersloh, Germany.
Reference:
P-38 Lighting in Action, 
Aircraft Number 109,
Larry Davis
Squadron/Signal Publications 
pg 45-55.