I've got both the E1L and the L4 and the bodies and heads are interchangeable. However please note that KL1 head (on E1L) and the KL4 head (on the L4) have different circuits and they are buck/boost and boost respectively. Both behave differently whereby KL1 head can accept 1xSF123, 1xR123a, 2xSF123, 2xR123a, 1x17670, and 2x17670 batteries. Whereas the KL4 head can only accept 1xSF123, 2xSF123, 1x17670 only.
Why use primaries only? Rechargeables are the way to go and its 'Guilt free' lumens and you will save alot in the long run. If you do decide to go the rechargeable way you need 2xR123a + 2x17670(for 2 cell body) + 1 Ultrafire WF139 charger that would set you back around $55.00