I've done a ton of research on this and here's what I found out so far
You really just can't change your regular bulbs to LEDS without adding a resistor to each one. It may also screw up your blinker rate and I've also heard people say just adding LEDS will strangly enough screw with your cruise control.
If you do try and add them I would suggest either SMT or 3 watt luxeon bulbs. These are the only ones that will be bright enough for motor vehicle applications. Luxeons are the brightest of all. They do make LEDS that are a combination of both SMT and Luxeon. you can find them at
www.superlumination.com or www.superbrightleds.com Super lumination site claims they are the very brightest and super bright leds come with built in load resistors
Do yourself a favor go to Ebay and buy the H3 LED ALTEZZA TAIL LIGHTS LAMPS. they sell them all ready to go. They also sell led signal and side marker lights for the H3 on Ebay.
Please if you do any of these things post with your impressions and Pm me I'm very curious to see hoew it works out for you
good luck hope your future is bright