Yup, that tailpiece should be enough to sink pretty much any luxeon you put in there. Just be sure not to rely completely on thermal cement to conduct the heat away, it's mostly there to fill in the tiny gaps between two metals. It's always best to make sure that the Luxeon sits as closely and as flush to the heatsink as possible.
Also note that the metal substrate on the Luxeon must be electrically isolated from both the negative and positive power connections.
BTW, how will you attach the tailpipe to your bike? Is 0.22 lbs a little hefty for a headlight body?