I have looked at this and am building several 2D lights right now:
1) P7 / Britelumens heatsink / Taskled d2Flex controller / 3 C NiMH or Alkalines in a PVC pipe sleeve with small or modified spring. 5 or 8 levels of P7 floodlight, focusable. Stock lens and reflector or upgrade to LOP/MOP for nicer beam pattern.
2) With mdocod or FM 6xAA holder and KIU bipin socket kit run a WA1164 hotwire. This is a modest overdrive, really simple mod. Requires lens and reflector upgrade.
3) Bored to take 8xAA holder (wquiles or others do the boring), will run WA1185 hotwire to 9.6V (not overdriven) but a very nice reliable incan. Use KIU base bipin socket and one of the 6xAA holders from mdocod or FM. Also can run the WA1164 bulb on this, pretty hot overdrive though. Requires lens and reflector upgrade.
I already did a 2D with a Malkoff devices 2/3D drop-in, very nice. This can be done with either a 2D/3D drop-in, and 2D alkaline/NiMH, or a 6xAA holder and a 4-6D drop-in with 6 AA Eneloop NiMH cells.
Another option is to set it up for an ashperic lens for super throw. Best to use a Cree R2 / heatsink setups for that, or possibly a Cree Q5.