Well I was gonna fit 12v mr16 with 3x3watt Cree LEDs in each bulb but decided to use those for my mountain bike lights.
They consist of 9x10mm high brightness LEDs per side.
I used the original grilles and just marked out the hole and popped the LEDs in and hot glued them in and wired em up with the resistors on the back.
I thinkmill do the mr16s soon tho as they are awesome in the daytime but I'll need to fit a dimmer for when the dipped lights are on during the dark hours.