Not exactly drop in. Would be nice to find a really high performance 1156 LED true "drop in" but I haven't seen one yet
If you cut a hole in the back of the light, the black plastic half of the assembly, exactly the diameter of the bulb just under the lip (the second widest point in the image above) when the bulb is dropped into that hole snugs against the glass reflector perfectly and concentrically when the reflector is screwed back on.
Direct wired to the harness it works wonderfully. The circuitry inside makes it flicker free, good light at idle, and very good light at speed. Nice spread angle looks natural as well.