If you want something that doesn't generate as much heat as the KL4, and gives you more runtime and about as much light; you can convert the E2D head to accept an Aleph light engine.
What I did was bore the head out to accommodate an IMS 17mm reflector. This little reflector puts out a nice beam. I haven't tried it with a McR16 yet. You could also use a McR20, with a bit more elbow grease and a thinner lens. After you bore the head out to accommodate the reflector of your choice, you'll need to "chase" the existing 13/16-20 threads with a tap. I use a bottoming tap.
Once you do this, you'll have an E series head that will take any Aleph LE.
Oh, I forgot about the curved lens in the E2d. It will make life easier if you swap to a flat lens. I've done many of these mods on E1e's, since the stock incand output is so weak.