I'm not sure if I wrote in other threads about this, but I made some LED conversions for friends' Sabrelights ages ago (when Cree XR-Es were close to the cutting edge of performance).
On the mechanical side, I used a section of 28mm copper pipe with a copper disc (older pre-steel UK 2 pence piece Dremeled flat) soldered in as a base. The battery contact was a large conical battery contact spring with a wire soldered to it (the wire passing through a hole drilled in the disc). I coated the wide end of the spring with a little JB Weld for insulation, then when that had cured, the spring was JB-welded onto the disc with a layer of epoxy to make sure the rest of the spring couldn't contact the disc if compressed.
I added a rim of JB Weld to the pipe end to help stop scratching of the inside of the bezel.
Electrical contact to the insert body was by a wire added when soldering the base on.
IIRC, electrically, I just used a pair of AMC7135 regulators to give 700mA, and the optic stayed cool enough when running.
The optic I used (a fairly long conical one which gave a good spot beam with an XR-E) allowed space for the 7135 board to be epoxied to the inside of the shell. Modern LEDs with shorter optics might need some kind of platform to raise the LED so the optic was close to the bezel.
The end result looked reasonable, if somewhat old-fashioned, and the copper body made a good heatsink. The only minor annoyance was that the tips of the U-shaped lower battery contact 'bar' could need bending inwards very slightly to avoid the chance of the insert being pushed between them, which meant that the bar might need pulling out when changing cells, as the clearance between the tips was less (the bar material was surprisingly stiff, so bending was more of a vice-and-hammer activity than just using pliers, so there wasn't perfect control about how bent things got).