6 volts from 2 CR123s will smoke the Luxeon in short order. You could try a Pila 168s Li-ion cell which is a little closer voltage-wise for direct driving a Lux 1, but is still risky.
Proceed at your own risk.
Edited to add: The L1 uses a boost only circuit, which is located in the body tube. The head itself is "dumb" and only contains the Luxeon.