I believe this is the large head 7D model. Has any one hotwired one of these? I'm looking for some ideas. Thanks.
Ah, now you say the magic word! We thought you were looking for a
puny bulb...
An ROP low should do nicely as a start -- not sure about the ROP high, it may instaflash on hot batteries, but if you let them rest, I think it could work. (All depends on the resistance of that light, really...)
You could also use a PR to bipin adapter, which opens up a wider range of options, but may not focus well (I have no idea the focus range on a Kel-lite, but filaments are typically farther forward in a bi-pin to PR adapter than the original bulb -- your light may or may not be able to compensate.)
Or you could load it up with 26650 or 26700 cells for something around 18-24V, and see what kind of bulbs will work out for that -- maybe one of the PR base bulbs used in the cordless-drill-style flashlights, or of course some of the badder bi-pins.