Apologies, I don't have a vice currently to be able to pull the tailcap and try to get some measurements.
I don't know of any decent chargers that charge 3 26650s simultaneously. There was a vendor that posted in the classifieds boasting about a 3x 26650 charger, but it didn't look particularly good. I'd say get 2 (or 3) of the Nicore i4s, or XTAR XP4cs.
You could probably get away with protected cells if you want, because the spring at the bottom and top have probably 1/3" of play with my king kongs in there. I did have some cheaper 26650s that were wrapped twice, and they were difficult to get in and out (it created a vacuum of sorts). It's worth noting most overhead divers would prefer the longer run time with the possibility of damaging their cells to protected cells in which the lights go out immediately. A little bit of light is worth a whole lot more than no light in a cave.
Finally, I just got a second one of these cans (from a different vendor), and it seems they changed out the cable for a shinier almost bike lock feel cable. Not sure if it's better, but it is different from the one received a few months ago. The branding is also slightly different (marked "Brinyte ELF-TSD3000").
I'll be testing the new one out in the next month or two when I get my drysuit and have time to hit the quarry.