For disassembly of the 3rd Generation MagLites, watch this great video from MagLite Mod God/Guru Old-Lumens :-
Video by Old-Lumens
I'm not so sure that you can drive that same 2xNiMH driver with 6 cells without the driver going though.
I have zero experience with the LED MagLites though, so I may be mistaken on that point.