That looks to be quite an ambitious project, but one well within the O-L scope !
The XM-L2 sounds like a great choice, as the higher Vf will likely better suit the over 5V when those NiMh are fully charged. You should be able to maintain regulation until the cells are depleted.
Three P60 reflectors will fit in a Mag D cell head with a little trimming (ok, a lot of trimming, lol), and the King is the same 52mm head AND is deeper than the Mag, so they only need trimming on the sides where they intersect and don't need to be shortened at all (other than chopping off the threads at the bottom)...
I'm watching with interest. Are you going to detail the driver mod again for the people as unfortunate as myself who did not understand it the first time you did this and whats the actual size of the batteries? I love the comedian OL. Quote, ''It's so ugly I had to slap it when it looked at me'' unquote. Not quiet sure what your referring to here but for some reason I'm still laughing. Thinking about it should I be worried? Cheers.
Being that you're swapping emitters you get a lot more flexibility to set the spacing the way you want, much easier than dealing with 3 on a single PCB. Cutting the p60 reflectors it might be less fiddly to spread them out so that the only cut you have to make is at the outside edge so each reflector only needs one cut. The one I'm working on is with a 3-up board, and the reflectors are gonna have to be cut to match the cut on their two neighbors...
Well crap... mine has thwarted everything I've thrown at it. Strap wrench, heat, you name it. Another user mentioned theirs had red loctite, there must be two different batches of these things.