IRA, BigC is right - the G2Z uses the same head as the G2, just a different body.
A Malkoff drop-in will fit any of the C, G, P or Z series from Surefire because they all use the same head - the differences are in the cut of the bodies.
Additionally, a fair number of people post about how deliriously happy they are with their Malkoff + Z flashlight combo. :twothumbs
-Trevor