The design of the E2DL/E1B/KX1/KX2 heads are all the same. You have the front outer shell which holds the optic and a lower shell that screws onto the flashlight body. Sandwiched in between those is a middle chunk of aluminum that has threads on both ends that holds the LED, driver board, and positive/negative contact plate for the battery. The threading/size of ALL of these components are compatible.
This means that if you really like the electronics of the E1B, but like the looks of the E2DL, you can just switch the middle "light engine" piece between the two. You could also just get away with switching the front outer shell (that holds the optic) and keeping the bottom parts intact.
It is sometimes very difficult to get the head apart, and you don't know if you are going to unscrew the front part from the middle light engine/lower shell OR if you are going to unscrew the lower shell from the middle light engine/front shell on the first go. From there, you can remove the middle piece from the remaining front/lower piece.