Congratulations on your retirement!
The heyday of the LED conversion is long past. This heyday was a relatively brief period of time after the introduction of bright, practical, and cost-effective white LEDs (and associated drive circuitry) but before many of the older, larger flashlight companies adopted LEDs. I bought several LED conversions for Maglites during that period. One is still going strong today, one seems to have been misplaced, and one fell victim to battery leakage (the great bane of alkaline batteries and all devices that use them). If I recall correctly, they were the Nite Ize 1W LED drop in replacements, which are still sold today, and are suitable for use in most C or D cell flashlights using anywhere from two to six cells. While not particularly bright by modern standards, I found/find them to be perfectly adequate for indoor use.
If you're looking for the best light to have on hand in the event of a power outage, a modern AA LED light with a range of brightness levels and a large pack of lithium batteries takes up very little space and puts you in a good position for the next 20+ years.
If, as Juan says, you wish to keep your old Maglite for sentimental reasons, you will still be pleasantly surprised by the performance of the drop in LED conversion vs. the old incandescent bulbs, especially when it comes to battery life.