It all depends a bit on the lighthead.
If it is one of the first, the head was bigger than the later ones. depending on the inside diamter, you can select the optics.
In the smaller ones, I used 3 XR-E's with fraen reflectors and overdriving them at 1.2A, while the bigger one could support 3 XPG's with ledil LXP optics. I just re-used the original heatsinks, although I modified one of them slightly as it had some metal sticking through the PCB to make contact with the LEDs. I just removed these pieces and was good to go.
If you can post a picture, or a link to a picture of your particular head, we can be more precise. Giving the inside diameter and the available height above the heatsink helps to determine the possible optics.
that looks look yet another version that the ones I've seen (typically greenforce), but the inside diameter allows for using ledil LXP optics if you have enough height available.
This link can help you determine the maximum diameter of the optics depending on how many you want to use.
just divide the inside diameter by the ratio that is mentionned for the number of circles/optics you want to use.
47.3/2.16=21.89mm diameter per optic if you want to use 3 LEDs.
using the dealextreme driver sku 26110, you can drive 3 leds in series from a 12V greenforce pack. If you want to upgrade it to 1.5A, you can just solder a 1ohm resistor in parallel with the sense resistor (next to the black wire of the driver).
It is suggested to heatsink the driver somehow, although I didn't test it without heatsink, so I don't know what would happen if you don't.