Do keep in mind that if those heat-sync "ribbons" are all crammed inside the back-cover of the housing, they won't do a whole heck of a lot to dissipate heat.
Depending upon how much heat they generate, you may expect a pretty short life out of the bulbs as a result.
I'd make an effort to keep those in open air, but still seal the opening to the housing around the base of the bulb somehow..
Still, I'm very curious to hear about the performance of LED in our Marks. I look forward to updates on this one, good or bad..