I don't think you will be satisfied with your work if you follow this design. It will not last long without heatsinking. Instead of using a bulb and cutting the wires (I've done that with 5mm leds and it isn't worth it)---why don't you thermal epoxy that K2 to a heatsink (or if you're trying to do this cheap, a chuck of metal) and solder wires from it to wherever the wires which go into the bulb holder go.
Also, whatever light you're using the PR base bulb base in---if that reflector was designed for a PR based bulb, it will focus better with the K2's height lowered --not raised like your design--
The whole--no resistors direct drive thing is also something I've done on several lights(but not without considering vf, battery chemistry, and wiring resistance). Remember--this is an LED not an incan light. The voltage isn't as important of a factor as the power supply's ability to supply current at it's voltage. You must consider your power source, and the forward voltage of your led. If you don't know it, put it in a circuit and measure the resistance, and source voltage, and use ohm's law for a quick easy answer. If you use alkaline batteries--2 cells won't sufficiently power any current K2s. The lowest vf binned I've seen are ***K, which you can run off 3 cells. Most K2s have higher vfs, but you would be wise to measure your current (again you really need to find the vf of your led. This information is critical for everyone who mods lights).
If you want to give it 2 cells---try your design and I'm afraid you'll be dissapointed by how dim it it. If you want it to be bright, properly affix it to a sufficient heatsink, drive it to spec (at the recommended current), and make certain it sits in optimal position relative to the reflector or optic used.
