It's easier to mod the old 1st gen L1 head than the E1e head to LED. More expensive - you have to get an L1 first, and the old ones are getting very rare - but makes for a better result with made-for-LED heat sinking and is slightly smaller than the E1/E2 head since it has a cutout around it which also gives better grip. I currently use an SSC modded old L1 head on an E1e body. My favorite and most carried light anymore. I use a two-stage McE2s switch on it. ~30L low, 150+ on high. I recommend using some sort of resistor because it direct drives the LED in this set up - there is no driver in the L1 head or E1 body.
If you really want to mod your E1 head, then I think somebody here was working to make a Rebel solution. The rebel can fit on a post like the E series bulb. I have not seen it being offered yet. I think it can be done, the heat sinking on a post just won't be as good as an L1, KL1, or KX1 head.