Before I reassembled the drop-in, I wiped some hazing off the reflector with some chrome polish and inadvertently removed some of the reflective finish. I needed a new reflector.
There is a recess around the top of the M61 heat sink that the top of the stock reflector sits in – that’s the flat part of the reflector. I put a GITD (Glow In The Dark) O-ring in the recess and it held the McR-20S reflector perfectly. The new LED is mounted on a thinner circuit board than the Malkoff board, which in this case helps with the reflector placement. The bottom of the reflector (with a thin insulator) rests on the LED board. The other end of the reflector is flush with the end of the heat sink.
The beam is very nice. Compared to a M60 or M30, there is less of a hot spot and more spill. The stock M61, IIRC, didn’t have as much of a hot spot compared to the McR-20S.
So far in this mod, I have destroyed the Malkoff M61 driver board and damaged the reflector. But now I’m happy with a drop-in that has a great heat sink, a great beam and three modes. It’s now in my current favorite flashlight, the Surefire C2.