The XR-E Crees have a very narrow beam pattern quite unlike a buld. That fixture was designed specifically to have a bulb in it with the associated pattern. Working in the automotive field at times, I generally warn everyone to stay away from trying to put LEDS into bulb fixtures. If you get in an accident, someone is hurt, and you have non-compliant lights, not only are you responsible, but your insurance company is going to be non-to-happy with you. Are you willing to take that chance?
The other issues is I don't want to be driving behind you and be blinding when your light emits a rediculous amount of light in some certain direction.
The standard were developed to balance visibility with not blinding someone. They are also meant to not be overly distracting by throwing light in too wide an area. They are also meant to put out the right amount of light in all cases. When you take that trip through the desest just after sunset and your car is really hot, are your Amber LEDs going to put out sufficient light? Yes car manufacturers do design to those specs and yes, they are tested to them as well....the OEM designs at least. Put any non-conforming thing you bought off the web/parts store into it and you are on your own....figuratively, and if you have an accident, perhaps literally as well.