The idea is to fit a XM-L star on the stock pill without boring it adittionally and hoping the reflector is from aluminum. It should be since the incandescent bulb might get too hot for a plastic reflector or perhaps not if it uses a poor bulb.
Also would like to use the KD 2,8A linear driver (probably modded to 2,45A or less) and powering it by classic alkaline D cells perhaps Ni-mh in future. The question is would the alkalines be able to sustain 2,5A draw for a extened time?
What's on the other side of the pill? Suitable to install a driver?
About an hour at 2.5A with decent alkalines, a lot less with cheapies. Given the cost of D Duracells round here it would not take long for rechargeables to be very well worthwhile.
The voltage is likely to sag too low to light the LED in less than that. The Duracell chart is discharge to 0.8V - depends on how gracefully the driver handles low voltage.