I replaced the original guts of my bullet light with parts from a newer style LED light. The LED light's control/switch didn't work, but it was a donor for the LED cluster and the battery holder. The old bullet I found in a bin'o'stuff at a bike repair shop for around $3.00. Unfortunately the plastic internal parts were very brittle to begin with, and there was a lot of corrosion on the old 'spring' contacts for the batteries. The power loss on the old bullet was ridiculous. Two new 'C' cells giving 3.37v combined, and less than 2.0v were making it to the bulb. The light looked good but didn't do much more than that.
So, to widen the hole for the lamp holder in the reflector I used the dremel with a sanding drum and widened the hole a little at a time until the LED cluster would just barely slide into it. The LED cluster is epoxied in place with JB Weld.
The original switch on this old bullet was salvageable, I drilled a small hole in the tab on the off-side of the contact to solder the pos/+ lead to from the battery box. I spliced on to the old wire and connector and ran that in to the LED Unit, then neg/- to neg/- on the battery box. Soldered and heat-shrinked every connection. There's no loss now, 6.56v at both the batteries and the cluster. I wrapped the 'AAA' battery pack in some foam and packed it into the housing. When the front is closed and latched, everything is nice and firm.
The difference in brightness is staggering, can't wait to see what it's like on the road at night.