Since you do not know the bin, and it is not marked on emitters, you have some estimating to do. If you have a voltmeter, it will be easier.
Step 1 - Temporarily, heat sink the emitter - somehow. This is the most critical thing you will ever do. This might be some thermal grease to the top of a 1/4 inch bolt or some copper rod, etc.
Step 2 - Obtain some kind of battery holder which can hold 3 or 4 C or D cells in series. Also some alligator clips.
Also pick up some 1 and 2 ohm, at least 1 watt resistors. The big axial flameproof ones from radio shack are great for testing.
Strongly consider wearing sunglasses for the testing.
Step 3 - Start with 2 cells in series, and hook them up directly to the Lux III using the alligator clips. Be sure to hook the positive side of the batteries to the anode of the Luxeon - this is the side with the small hole in the secondary little electrode sticking out.
It should light up at least dimly.
Step 4 - Now put 3 cells in series, a 1 ohm resistor, and ideally your voltmeter also in series. It will probably read approx 200 - 400ma. Remember this setting.
Step 5 - Now the same setup with out the resistor - probaby will be around 600 - 800ma. A good place to stop.
Step 6 - Now use the same setup with 4 cells in series and 2 ohms - should also be in the 600 - 800 ma range. If you are much above this, consider adding more resistance.
You are now very similar to the setup of using a "2 x 123 cells, a small resistor, and your nice new Lux III. All without the pain of destroying it.
If you do not have a voltmeter and do not have access to one through a friend, consider using 2 ohms and 2 x 123 cells anyway. While not optimal, it is unlikely that someone would sell you a very low Vf bin Lux III without telling you and charging quite a premium.
Direct driving 2 x 123 with no resistor in a Lux III is done by some people, but the heat sinking needs to be reaaallly good and battery life will be not very good.