Reminds me of my prototype I built back in 2007 (pictures below hopefully), this is a Cree XR-E P4 (or Q2, don't remember which now, bought both around the same time), STUFFED into a hex bar (very similar to your current design), but this was much smaller. This is still my "go-to" helmet light, weighs next-to-nothing without the mount.
This is using the Polymer Optics hexagonal optics, and I sized the bar just larger than the optics (forgetting to take into account the holders, I hoped I wouldn't need those... they do, or they are impossible to align)....
Bottom line, this was a rough prototype (zero measuring done, mounted in a mill and went to work) so it was a bit too short and small to fit the electronics (simple AMC7135 700mA regulator board) so that's what you see "wrapped" in red externally (I wrap the cable around the mount to "strain relief" it, it's been through some heavy trails and tree-snags and keeps working, but definitely NOT rainproof.
Actually milled it out in about 4 hours on a manual mill, although getting the internal "hex" corners was challenging without breaking an 1/8" milling bit. Lighthead is actually sealed (silicone around the lens/front, and cable exit) but the controller is just wrapped in electrical tape.
Uses a Deans Micro connector which has been great.
I intentionally extended the lens out the front (but more than desired) as it gives great side-spill for when I use it as a road light (more than I do off-road).
Hopefully the pics will come through, haven't tried this method before (I used to host my own website which made it easier).
Oh, wall-thickness around the lens is roughly a fingernail (not even a thumbnail)... about 1/10mm.
The light-head "mounts" to the base via a zip tie which when pulled tightly sits in grooves on both parts (I couldn't get it out just now even prying with a screwdriver, had to cut the tie, but I've got thousands of them, LOL), and the light-head mount vertically pivots, not nearly as nice as the one you are making here though, I just slapped flat piece of aluminum to 2 slightly milled (to fit inside each other) u-channel I had handy and popped in a couple of "rivet pivots". Works great though, but ugly.
It is EXACTLY 1 "American Quarter" long. No noticeable heat problems (while riding, otherwise when standing still it gets pretty warm pretty quickly), it's only running 700mA, and when strapped to the aluminum base has quite a bit of thermal path (but when not mounted, I don't keep it on long), the LED is actually soldered to a copper baseplate which fits inside the light-head and is arctic-alumina'd to the base to spread the heat further from the LED quickly.