I claim the ornamental design for an anti sway bar drop block, as shown.
FIG. 1 of the drawings is a perspective view showing the right side, bottom, and back of an anti sway bar drop block embodying the design of my invention;
FIG. 2 is a bottom view;
FIG. 3 is a right side view;
FIG. 4 is a back view;
FIG. 5 is a front view;
FIG. 6 is a top view;
FIG. 7 is a left side view; and,
FIG. 8 is a reduced right side environmental view of the anti sway bar drop block. The broken lines are for example only and form no part of the claimed invention.